One of the manga that take place in the Touhou series (mainly known for the games by Team Shanghai Alice).
Taking place between part 10 and 10.5 of the doujin game series, Silent Sinner in Blue follows Yukari Yakumo as she prepares Reimu for a new threat originating from the Lunarian capital of Gensokyo's moon. At the same time, a lunarian Rabbit is also sent down to Gensokyo to warn Eirin Yagokoro and Kaguya Houraisan of the current state of the Lunar capital, and to try to stop Yukari from achieving her true goal.