Chocotto Sister

Chocotto Sister (ちょこッとSister) is a manga series by Go Zappa with illustrations by Sakura Takeuchi. It is published by Hakusensha in the magazine Young Animal and collected in 8 tankōbon volumes. The series has been adapted as a 24-episode anime by Nomad, airing in 2006.

Plot
The story centers around a Christmas wish made by a young Haruma Kawagoe, who was eagerly anticipating having a baby sister, after his mother suffered a miscarriage followed by a hysterectomy. Several years later, when Haruma is a college student, a woman on a flying motorbike claiming to be Santa Claus delivers his wish, a younger sister. When he remarks that he made his wish a long time ago, "Santa" replies that making a little sister takes a lot more time than just making an android, takes his signature for delivery, and departs. Haruma now has a little sister, who comes with her own instruction manual — a manual for how to be a little sister, that is. When she asks him to name her, he calls her Choko, which refers to the Japanese word for "manual".