Eientei is a large mansion hidden deep within Gensokyo's Bamboo Forest of the Lost where the Lunarian princess Kaguya Houraisan resides alongside her reliable advisor Eirin Yagokoro. Accompanying them are numerous youkai rabbits led by Earth rabbit Tewi Inaba and Moon rabbit Reisen Udongein Inaba, who protect the princess from danger. However, their primary purpose is to pound mochi every month as part of the Moon Festival, Reigetsusai.

From Kaguya's fierce rivalry with Fujiwara no Mokou and Tewi's mischievous pranks, to Reisen's serious yet fallible nature, even a secluded place like Eientei has no shortage of fun and hilarity.