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Mizuchi Miyadeguchi in Foul Detective Satori
More Character Titles
Capable of possessing people.
- "Unnatural Order is always bound to break somewhere."— Mizuchi Miyadeguchi (Cheating Detective Satori)
- "Ignorance is such a cruel thing. A youkai cannot fight a vengeful spirit, because inside, you're all the same."— Mizuchi Miyadeguchi (Cheating Detective Satori)
Mizuchi Miyadeguchi (宮出口 瑞霊 Miyadeguchi Mizuchi) is the main antagonist of Foul Detective Satori.
Mizuchi dislikes the lack of chaos in the current Gensokyo - and doesn't mind helping the "unnatural order" collapse.  She complains ironically that even the Human Village is full of youkai, arriving to the conclusion that maybe humans “lost” against youkai, an event only possible thanks to the irresponsibility of the Hakurei Shrine.  Furthermore, it seems she doesn’t want her actions to go unnoticed, complaining about how the Bunbunmaru newspaper doesn’t mention that Reimu Hakurei shut herself in the shrine thanks to her; affirming that she may have to "send the entire surface even further into the depths of terror" to achieve it.
- Capable of possessing people
She has the ability of possessing people, taking complete control of their body and even their abilities. Her victims have no memories of anything that happened during the time that they were possessed. Using this possession ability on Youkai will result in them falling in to a coma by draining all of their magical energy, this will not be the case on humans however, as unlike youkai, they are not composed of magic energy.  However, Fujiwara no Mokou also entered into a coma after being possessed, even though Mokou is a human. It looks like even though she is possessing someone, she doesn't have access to the knowledge the victim has, as she couldn't understand a thing about kappa technology while she was possessing Nitori Kawashiro. 
Mizuchi is a vengeful spirit that escaped from Old hell, prompting Satori Komeji to search for her.
Her full name is Mizuchi Miyadeguchi (宮出口 瑞霊). Her surname Miyadeguchi (宮出口) contains the kanji "miya" (宮), which can translate to "shrine" (in Shinto context) or "palace".
"Deguchi" (出口) is a term that translates to "exit".
Mizuchi (瑞霊) roughly translates to "young spirit". "Mizu" in this case is an archaic term that can be translated as "pure" or "young".
She has blue eyes and blue hair worn in a ponytail, and wears a white dress with red lines and black frills. She has a pair of handcuffs with one end being attached to her neck, with the ends being gold colored and the chains fading into white. She also wears a pair of white gloves, and her legs cut off at the knee into a flame-like white trail.
In Foul Detective Satori, Mizuchi takes possession of people and makes them fall into a coma by draining their magic energy. She picks her victims in the order of the series' incidents (Scarlet Mist Incident, Spring Snow Incident, Eternal Night Incident), meaning that she has been watching Reimu for a very long time. However, after Yuyuko, her next possession target should have been Suika due to the "Night Parade of One Hundred Oni Every Four Days" incident in Immaterial and Missing Power, why this was skipped is unknown, along with the Flower Incident (Phantasmagoria of Flower View). Mizuchi also started with the incident of Touhou 6, ignoring all the characters of the PC-98 era. Though this is likely because the Windows series follows a different continuity from the PC-98 series. She does it as part of her plan on taking “revenge on Gensokyo and the Hakurei Shrine". 
She appears to have no allies; she had received help from others only by deception, taking advantage of her ability to possess other people's bodies and manipulating friends and allies of the target.
Reference sheet of Mizuchi from Foul Detective Satori (monochrome)