Itsuki Hashima is a light novelist obsessed with little sisters, strictly focusing on them when he writes his stories. Despite his personality, he is surrounded by a tight circle of friends: Nayuta Kani, a genius yet perverted novelist who is in love with him; Haruto Fuwa, a fellow male author whose work has seen considerable success; Miyako Shirakawa, a good friend that he met in college; and Chihiro, his perfect younger step-brother who takes care of the housework and cooking. Together, they play strange games, go on spontaneous journeys, crack silly jokes, and celebrate each other's successes. However, each individual must also deal with their own issues, whether it is struggling to meet a deadline or coming to terms with traumatic events buried in their past. [Written by MAL Rewrite]

Akira's father, an archaeologist, has remarried, giving him a new stepmother and three stepsisters, Yuki, Nana and Miu. While on his honeymoon, Akira's father makes an archaeological find and decides to stay on site in order to supervise and leaving Akira at home alone with his new family members. After being discovered in bed with Yukie, his stepmother, Akira finds a box containing a scroll and three bottles. Using the knowledge his father taught to him, he reads the Sumarian language on the scroll and finds himself in a contract with the goddess Inana, who tells him to collect the love juices of his sisters in the bottles before the next full moon or else a terrible horror will befall him. (Source: ANN)

Cocoa visits her family, in the mountains, after quite some time again after her sister Mocha wrote her, through a letter, to come back soon. Her friends will have to spend a week in the town without her, while Cocoa has time with her family that she hasn't seen for a long time. But Chino, Cocoa's self proclaimed little sister, wants to go watch, with Cocoa and all her friends, the fireworks in the fireworks festival, which is coming up in less than a week. Cocoa decides to return early as she misses them all, but will she arrive in time for the climax of the festival? (Source: TMDB)

Haruma Kawagoe is an only child. A long time ago, at Christmas time, his mother miscarried the child that was to have been his baby sister. That night, young Haruma knelt down and offered up an earnest prayer: "Please make my mother well again, and please give me a little sister." Years have passed, and Haruma has nearly forgotten his prayer. But Santa hasn't.... one Christmas, when Haruma is least expecting it, he gets an unusual present - his sister. (Source: ANN)