Eirin Yagokoro

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() (ごころ)   (えい) (りん)
Eirin Yagokoro
jagokoɽo eːɽiɴ (♫)
Eirin Yagokoro IN
Eirin Yagokoro in Imperishable Night
Brain of the Moon
More Character Titles

Lunarian (God)


Making any drug.
Natural Genius.


At least 1500 years old, older than Lord Tsukuyomi and the Lunar Capital, possibly hundreds of millions years old.[1][2]




Eientei, was originally from the Moon

Music Themes
Official Games
Print Works

"Young children like yourself can't stand a chance against me, an eternal being. All the scarlet history that you've built up--- Divided by my history, the result is zero. From eternity's point of view, you are but a mere instant."— Eirin Yagokoro

(Imperishable Night Stage 6.)

Eirin Yagokoro (八意 永琳 Yagokoro Eirin) is one of the antagonists of Imperishable Night. She's a medical genius from the Moon, able to create even the Hourai Elixir with the help of Kaguya's power, the manipulation of eternity. She is living in exile in Gensokyo after choosing to stay with and devote herself to Kaguya Houraisan on Earth rather than take her back to the Moon. She was a very well-known figure on the Moon, having not only been instrumental in the founding of Lunar society with Lord Tsukuyomi, but also being its leading medical mind and the person in charge of the Moon's emissaries to the Earth.

General Information

She first appeared as the Alternative Final Boss in Imperishable Night, and she was stage 9 target in Shoot the Bullet. She is also involved in Legacy of Lunatic Kingdom.


Eirin is an enigmatic person surrounded by many mysteries and her answers regarding the mysteries about her are incoherent replies. She is generally a fairly pleasant person and is devoted to serving her ally, Kaguya, but she does not suffer fools gladly, and because of her incredibly high intelligence, she can come across as conceited, impatient and condescending at times to those not sharp enough to follow her explanations immediately. However, she also seems to lack general common sense, most likely due to her not living with humans.

Eirin illustrated in The Grimoire of Marisa.


Making any drug

She can make all sorts of drug/medicines, from medicine for the ordinary cold to drugs that can manipulate dreams. As one would expect, she is not able to make medicines that would require a physically impossible process in order to produce, nor can she make the medicine if she does not have the ingredients. Although she did make the Hourai Elixir, she made it using Kaguya's ability.

Natural Genius

Eirin is said to be highly intelligent and considers other people to be less smart than her. Furthermore, the Yagokoro family is said to be a line of medicinal geniuses and even among them, Eirin is exceptionally intelligent. Due to this, Eirin is rarely understood by others.


It is not specified in her profile, but Eirin reveals to Yuyuko in the Netherworld Team's Good Ending of Imperishable Night that she has drunk the medicine made with Kaguya's ability, in order to not die. Yuyuko's response and further narration cement that this is referring to Eirin having become immortal, from the Hourai Elixir.

Other abilities

Aside from her medical knowledge, Eirin seems to be very skilled in various forms of magic. For instance, in Imperishable Night, she sealed the whole Earth preventing anything or anyone from reaching or leaving it. Additionally, she replaced the real Moon with a fake one that was able to mislead the heroines with an illusion. According to herself, doing this was "hardly" her most powerful spell, meaning that she is probably able to use other types of sorcery that are far stronger than this[3].


After the events of Imperishable Night, Eirin has begun using her knowledge of medicine to act as Gensokyo's premier pharmacist, selling medicines at Eientei ranging from sleep aids to various cures. You can visit her like you visit a normal doctor, and she can even prescribe medicine for obscure illnesses. Her medicines are well known to work with no side effects, though youkai medicine and human medicine must never be mixed together. It's reasonable to believe her medicines come from the Moon or are developed with Lunar technology. The medicine is not only effective, but fairly priced. Fortunately, Eirin is not fussy about payment; she will most likely wait until you pay her. Still, it is believed that Eirin may have another reason for starting this business other than profit.


Bow and Arrow

Eirin wields a bow and arrow. Presumably, she uses it for spellcards.


A long time ago, Eirin was the Sage of the Moon; with her high intelligence and the aid of the former Princess of the Moon, Kaguya, she created the Hourai Elixir and gave it to her. As a result, Kaguya was exiled to Earth as a punishment for drinking the elixir. A few years later, Kaguya had been allowed to return to the moon and, along with other Lunarians, Eirin was sent to Earth as an emissary from the Moon. Eirin felt guilty because she herself wasn't punished even though she was the one who made the elixir. Her desire for redemption was so strong that she was ready to do anything for Kaguya, and so she killed all the other emissaries and decided to live on Earth with Kaguya as her own punishment.

After living a few hundred years hidden in the Bamboo Forest of Gensokyo, her whereabouts were discovered by the Moon, and led to the Eternal Night Incident, but at the time the incident was resolved, she came to know that even if she did not try to hide the Moon, the Lunar Emissaries wouldn't be able to come for Reisen. She has been living as a resident of Gensokyo ever since.

Character Design

Eirin illustrated in Perfect Memento in Strict Sense


Eirin is likely based on Ame no Yagokoro Omoikane no Mikoto (天八意思兼命), the god who thought of the plan to lure Amaterasu out of hiding. This can be seen by her spell card, and by the correlation between Eirin's sharp intellect and Omoikane's. (Takami-Musubi is also very strongly associated with intellectual facilities.) The interrelationships of various lunar figures presents a more interesting situation. Eirin is distantly related to the Watatsuki sisters, both based on mythology. In the third chapter of Cage in Lunatic Runagate, Watatsuki no Toyohime mentions that Eirin's participation was critical to the founding of the lunar capital, and that she was older even than Tsukuyomi. Omoikane is the son of Takami-Musubi, one of the great gods that summoned Izanagi and Izanami into existence, but it's unclear whether Omoikane was born before the creation of the Japanese islands, which also saw the births of Amaterasu, Tsukuyomi, and Susanoo. Regardless of whether she is "meant to be" Omoikane, Eirin clearly draws on Omoikane in many ways.


Her full name is Eirin Yagokoro (八意 永琳). The characters for Yagokoro (八意) literally means "eight minds" and Eirin (永琳), "eternal jewel". The number 8 in Japanese culture signifies the sacred and the infinite, and is often used indefinitely to mean "many" or "countless" (as in the Eight Million Gods). Gokoro is an ancient reading for , which could indicate something about heart or mind. So her whole name could mean "Intelligence of eternally clear brightness over infinitely extended area", referring her to be the "Mind of God". It is revealed in Silent Sinner in Blue that "Eirin" is merely her earth name, her true Lunarian first name being unpronounceable to the impure earthling tongue. Regardless of "Yagokoro" in both cases, she is strongly implied to be Omoikane.


Eirin has dark grey eyes, long silver hair, has a large braid on her back and carries a strange pair of bow and arrow. Her clothing is red and blue and is covered with constellation patterns. She also wears something similar to a nurse's cap.

Eirin's clothing has trigrams (broken and solid Yin/Yang lines) lining the bottom hem. They appear to be the complete set of trigrams used in Feng Shui, and match the set of trigrams on the Hakkero.



Imperishable Night
Eirin's sprite in IN

During the events of Imperishable Night, Eirin attempted to seal the passage between the Earth and Moon, which opens every full moon, by casting a spell that would seal the Earth inside a chamber (similar to a Chinese folktale about a paradise found inside a pot). She only meant to do this to protect both Kaguya and Reisen so that the emissaries coming from the Moon wouldn't be able to reach them, but this did not go unnoticed by the various Youkai in Gensokyo who enjoy the moonlight.

Legacy of Lunatic Kingdom

Eirin is involved in the backstory of Legacy of Lunatic Kingdom. The Moon habitants decided to make an invasion to Gensokyo with the intent of purifying it. Moon rabbits and mechanical spiders are razing the place and leaving a lifeless Earth. Gensokyo's humans can't fight by themselves, because a simple error means death, and it also looks like the youkai for some reason can't interfere with the purification, but Eirin planned ahead for such event and made a medicine that allows the user to see the close future. She sends Reisen to give the medicine to Reimu Hakurei, Marisa Kirisame, and Sanae Kochiya and resolve the incident. This medicine is the tool that allows the Pointdevice gameplay mode, in which the player cannot get hit once.


Eirin in HM
Shoot the Bullet

In Shoot the Bullet, Aya Shameimaru encountered Eirin on stage 9 and took photos of her danmaku.

Hopeless Masquerade

Eirin made a background cameo appearance in Hopeless Masquerade on the Human Village stage. She is seen sitting on a bench with Tewi Inaba, Kaguya Houraisan and Reisen Udongein Inaba drinking something.


Bohemian Archive in Japanese Red

Eirin has created a new medicine called the Kochoumugan (Butterfly Dream Pill), which guarantees that one will have a pleasant dream. She says that since the youkai of Gensokyo rarely suffer from physical ailments, she began developing medicine for spiritual ailments instead. This particular medicine is ancient, but humans who took it in the past often found their dreams too enjoyable and never returned from the dream world, so Eirin has weakened its potency and made it safe to use. She also has a variety which causes nightmares instead of pleasant dreams.

In the interview, Eirin remarks that only a few people have come to buy the pill, even though it was a featured article in Aya's newspaper. Aya admits she doesn't have many readers. She is curious who is buying the medicine; Eirin is initially reluctant to say, but then reveals that it was Alice Margatroid. Aya mentions that she tried the pill herself, but found the dream uninteresting. Eirin suggests that she try Kochoumugan Nightmare Type (a scene in Shoot the Bullet).


Kaguya Houraisan

Kaguya is Eirin's master and friend. She made the Hourai Elixir for Kaguya which resulted in her banishment. Feeling regretful, when she was sent to Earth to bring her back on the Moon, she killed the other emissaries and helped Kaguya with hiding herself. Now she serves Kaguya faithfully at Eientei.

Reisen Udongein Inaba

Eirin's servant. Eirin has employed Reisen's telepathic abilities to gain intelligence on the Lunar capital. She also sends Reisen to the Human Village to sell her medicine.

Tewi Inaba

Tewi made a deal with Eirin to defend Eientei in exchange for Eirin imparting her knowledge to the rabbits. Thus Eirin is an ally, employer and teacher to Tewi and Tewi appropriately addresses her as Master. Eirin realizes Tewi's importance to Eientei due to her control over the rabbits and despite Tewi's pranks, knows that Tewi is there whenever they really need her, should the circumstance arise.

Watatsuki no Toyohime & Watatsuki no Yorihime

Eirin was a teacher to both Toyohime and Yorihime. They both respect Eirin with much admiration even after Eirin became a fugitive. They both are also distantly related to Eirin through marriage to their unnamed husbands (one of the Watatsuki sisters was the wife of Eirin's grandnephew, while the other one was married to their son[4]),

Lord Tsukuyomi

Not much was known how close they are, however they both founded the lunar capital together, so they could have been in good terms. It's unknown if their relationship remains the same after Eirin's desertion.

Medicine Melancholy

After learning of Medicine from Reisen, Eirin goes to the Hill of the Nameless to meet her. Eirin takes an interest of her thanks to her poison abilities.

Minor Relationships

Alice Margatroid

Alice regularly purchases the Butterfly Dream Pill from Eirin.

Sakuya Izayoi

According to Eirin's profile, Eirin was very surprised to see Sakuya during the events of Imperishable Night. Though what relationship they have are unknown since only Eirin knows the reason why.







Spell Cards

Name Translated Comments Games Stage
Total: 18
天丸「壺中の天地」 Spacesphere "The Cosmos in a Jar" IN St. 6A: E/N/H/L
覚神「神代の記憶」 Awakened God "Memories of the Age of the Gods" IN St. 6A: E/N
神符「天人の系譜」 God Sign "Genealogy of the Celestials" IN
St. 6A: H/L
蘇活「生命遊戯 -ライフゲーム-」 Revival "Seimei Yūgi -Game of Life-" IN
St. 6A: E/N
蘇生「ライジングゲーム」 Resurrection "Game of Rising" IN St. 6A: H/L
操神「オモイカネディバイス」 Leading God "Omoikane's Device" IN St. 6A: E/N
神脳「オモイカネブレイン」 Mind of God "Omoikane's Brain" IN St. 6A: H/L
天呪「アポロ13」 Heaven's Curse "Apollo 13" IN
St. 6A: E/N/H/L
秘術「天文密葬法」 Esoterica "Astronomical Entombing" IN St. 6A: EN/H/L
禁薬「蓬莱の薬」 Forbidden Medicine "Hourai Elixir" IN St. 6A: E/N/H/L
薬符「壺中の大銀河」 Medicine Sign "Great Galaxy in a Jar" IN St. 6B: E/N/H/L
「天網蜘網捕蝶の法」 "Heaven Spider's Butterfly-Capturing Web" IN
薬符「胡蝶夢丸ナイトメア」 Medicine Sign "Butterfly Dream Pill - Nightmare Type" StB St. 9
練丹「水銀の海」 Elixir "Quicksilver Sea" StB St. 9
秘薬「仙香玉兎」 Secret Elixir "Lunar Rabbit Incense" StB
St. 9
永夜符「蓬莱壺中の弾の枝」 Eternal Night Sign "Bullet Branch of Hourai in a Jar" Co-owner with Kaguya VD
Nightmare Tuesday - 1
永緋符「墜落する壺中の有頂天」 Eternal Scarlet Sign "Plummeting Bhava-agra in a Jar" Co-owner with Tenshi VD Nightmare Tuesday - 3
永輝符「大きくなる壺」 [5] Eternal Shining Sign "Expanding Jar" Co-owner with Shinmyoumaru VD Nightmare Tuesday - 5

Additional Information

  • Eirin's profile states that she killed the other messengers sent with her. Kaguya's profile describes these messengers as "emissaries". Later official works would state that moon rabbits are trained as lunar emissaries, and it is unconfirmed if any of the emissaries were Lunarians. Given that rabbits are viewed merely as tools by the Lunarians, this may explain why the severity of murdering the other emissaries isn't emphasized whenever Eirin's crime of helping the princess comes up. Eirin has also made it clear in both Cage in Lunatic Runagate and chapter 2 in Silent Sinner in Blue that she has no qualms with killing moon rabbits should situation make her go to such lengths.
  • Eirin has a Spell Card named "Apollo 13" after the aborted third American moon mission launched in April 1970. The spell card's spell sign is "Curse of the Heavens", and seems to imply that it was Lunarian magic, not mechanical failure, that critically damaged the spacecraft and forced it to abandon its lunar landing so as to forestall the "invasion". It's also stated that the Lunarians know why the number 13 is cursed. Eirin in Silent Sinner in Blue reveals that the Apollo series failed because the sun ("Apollo") is incompatible with the back side of the moon, and Cage in Lunatic Runagate's 2nd chapter mentions Lunarian technology while talking about the humans' failure to establish a base on the moon, implying Lunarian sabotage.
  • Eirin had recently developed a medicine called Kochoumugan (Butterfly Dream Pill), which guarantees the person who takes it will have a pleasant dream once they fall asleep. The medicine was featured in an article in the Bunbunmaru Newspaper, but still remains fairly unpopular (mostly due to the fact that the paper itself isn't too popular). There is one customer, Alice Margatroid, who has returned numerous times to purchase the medicine however, although the reasons why were never disclosed.
  • In Tibetan Buddhism, the bow held in the right hand with an arrow in the left (as Eirin holds them) is a symbol of wisdom as a means of projecting method or skillful means.
  • The bow and the arrow are a possible reference to the huntress and Greek moon goddess Artemis (sister of Apollo; In Imperishable Night, ZUN made a joke about Apollo being the sun god, so he surely knows about Artemis). Artemis (or her bow) sometimes represents the crescent moon, symbol of full maturity in the cycle of life (it suits Eirin very well).
    • Artemis is often assimilated to Selene (the personification of the moon), which is the root of Selenium, a non-metal antioxidant sometimes used as a medicine but toxic in large quantity to human beings. Antioxidants are known to improve life expectancy.
    • Ursa Major, one of the constellations on Eirin's clothes, was originally Callisto, a servant of Artemis.
    • It is also confirmed that ZUN is aware of the bow representing the crescent moon. In Cage in Lunatic Runagate Chapter 5, Yukari is unable to see the crescent moon due to a storm, and wonders if it's because there is no one on the moon who wields a bow anymore.
  • In Chinese mythology, Houyi was a god of archery banished from heaven. He was married to Chang'e, Kaguya's Chinese equivalent. According to legends, he received the last two immortal elixirs from Xi Wangmu of Kunlun mountains in the west. Chang'e drank them both, who then ascended to the moon.


Official Profiles

Imperishable Night - キャラ設定.txt
Eirin Yagokoro IN  ○6面ボス 月の頭脳

  八意 永琳(やごころ えいりん)
  Eirin Yagokoro









Stage 6 Boss, Brain of the Moon

Eirin Yagokoro

Species: Lunarian
Abilities: Making any drug. Natural Genius.

She's a person from the moon. That means she's an alien. She has lived on the Earth for a long time. Her relationship with Kaguya dates back to their days on the moon.

The Yagokoro family is a line of medicinal geniuses that have been living on the moon for some time. Even among them, Eirin is exceptionally intelligent. She is much smarter than humans, which makes her rarely understood.

In truth, she has power well beyond that of Kaguya's. She saves her power and maintains it at a lower level out of respect for Kaguya.

Long ago, Eirin was one of a party of messengers who were sent to bring Kaguya back to the moon; the crime for which she was exiled to Earth had been forgiven. For some reason, she helped Kaguya kill all the other messengers instead. To ensure that the earthlings who lived with Kaguya would remain silent, she bribed them with the Hourai Elixir. The elixir had the power to make people immortal. None of those earthlings consumed the elixir, however, and died shortly afterwards.

It was later discovered that they were murdered.

More detail is available in Kaguya's profile.

Eirin is very surprised to see Sakuya, but only Eirin knows the reason why.

Eirin 八意 永琳(やごころ えいりん)


Eirin Yagokoro
Lunarian/Ability to the extent of making any drug.

A former Lunarian who hides in Eientei along with Kaguya. She is the "Brain of the Moon"
whose intelligence doesn't end at being well versed in medicine handling.
She's called the "Sage of the Moon" but escaped to the surface
due to the incident revolving the Hourai Elixir.
Now she seems to be using her knowledge
to work as a pharmacist and doctor, but...?

Official Sources

Official sources


  1. A castle to return to - booklet: 原作者ZUN氏に聞いたところ(酔っぱらった時に聞いた答えだが)、永琳や輝夜の年齢は億単位だそうだ。
  2. Strange Creators of Outer World Vol. 2 - Imperishable Night's Fragment of Fantasy
  3. Imperishable Night - Barrier Team's Scenario.
    Reisen: Ah, you're talking about the moon? That's my master Eirin's most powerful spell. It makes this Earth into a giant, sealed chamber. Do you get it now?
    Eirin: Also, about that full moon-erasing spell. It's hardly my most powerful one.
  4. Cage in Lunatic Runagate/First Chapter
  5. Incorrectly displayed in-game as 妖風符「土着蝶ストーム」(which is Yuyuko and Kanako's card from a previous scene). Real name was later revealed in SCoOW Volume 7.