Yuuji Tsubakihara lives with his childhood friends, the twin sisters Yuna and Nina, and their mother Mira. When the shy Yuna confesses that Yuuji is her secret first love, it triggers a chain reaction of passion that involves both sisters and Mira, blurring the lines of their family dynamic through a series of explicit encounters.
As the school festival approaches, Yuuji finds himself as the tie-breaking vote between opening a Demon Café or an Angel Café. However, the festive preparations are overshadowed by his escalating intimate relationship with Mira. After a series of secret encounters and a heartfelt confession of love, Yuuji and Mira decide to move past their familial roles, only for Nina and Yuna to discover them and demand to join in.