Kkhta Eirin

In the past, Eirin was sent by Lord Tsukuyomi to retrieve Kaguya Houraisan after she fled the Moon for Gensokyo, but upon meeting with her decided to stay in Gensokyo with her instead. Growing suspect of the Lunarians' plans, Eirin developed a special elixir to counteract the effects of the Moon's maddening rays and had it spread across Gensokyo in the form of rain.