Ojou-sama no Doki-doki Daisakusen: Norowareta Kurenai no Yakata

One day in the Scarlet Devil Mansion, Remilia and her staff have a tea party with Marisa Kirisame, Yuyuko Saigyouji, and Youmu Konpaku as "guests" (read: they invited themselves). Intent on proving her peaceful intentions, Marisa shares some of her new "Shroom" brand tea with everybody.
Later that night, everybody finds themselves chibified, and the mansion warped and overrun with monsters. It's up to Remilia, now severely weakened, to fight her way through her own home and solve this incident by tracking down the culprit.
In the meanwhile, Flandre has to fight the powerful being that she has summoned in her room, and Yuyuko goes on to explore the mysterious 10-floor tower that has appeared in the mansion.

Can the trio uncover the truth behind this incident?

Résumé

Ojou-sama no DokiDoki Daisakusen is a fan-made Touhou Project platform action game, developed by BlueMica. It features Remilia Scarlet as the protagonist and Flandre Scarlet as the second protagonist. Saigyouji Yuyuko is also a playable character.