Three Fairies of Light
The Three Fairies of Light (光の三妖精 Hikari no San-Yousei), or the Three Fairies (三妖精 San-Yousei) for short, also called the Three Mischievous Fairies, are a small group of fairies composed of Sunny Milk, Luna Child, and Star Sapphire. They are known for causing mischief to humans by playing pranks on them using their powers. They are the protagonists of the Touhou Sangetsusei manga series, and the antagonists of Fairy Wars.
The "three lights" refer to the sun, moon, and stars, the most clearly visible lights in the sky. It is from these lights that the fairies derive their power and after which they have been named. Many of their spell cards reflect how they derive their power. These three lights are also referred to in the name of work in which they appeared; The title of the manga, "Sangetsusei" (三月精) is a wordplay, which loosely means "sun, moon, stars" respectively based on pronunciation, whereas "三精/Sansei/Three Sprites" used to be the old name for these three heavenly bodies put together. san (三) can also mean san (サン, Katakana transliteration of English "sun"), getsu (月, "moon") stays the same and sei (精, "fairy") shares the same sound as sei (星, "star").
Illustration of the Three Fairies in Bohemian Archive in Japanese Red
The Three Fairies of Light as seen in Oriental Sacred Place
The Three Fairies of Light in sleepwear as seen in Strange and Bright Nature Deity
The Three Fairies of Light cameo with the moon flag in Silent Sinner in Blue