Manga by author Kindaichi renjuurou

One day, on a whim, 20-year-old Minato dresses up in her friend's cute high school uniform and goes out briefly into the city. To her horror, she ends up running into her stepbrother, Tooru, who is actually only months younger than her. Since he's cute, and a notorious player, Minato has had to deal with constant jealousy and suspicion from other girls all through their school days. Amazingly, she manages to convince Tooru that she's actually someone who just happens to look a lot like his sister. He is so convinced that he starts trying to date her and, for various reasons, she goes along with it. What started as a simple joke is now evolving into the biggest lie Minato has ever told!

The story is about Hare, a 10 year old boy who lives with his mother Weda in a small village in a very strange jungle. Hare's mom is a bit of a "party girl" and likes to sleep in all day and party with her girl friends all night. Things change one evening when Weda comes home with a little "playmate" for Hare, a pretty little girl named Guu. But when Hare wakes up the next morning, Guu has "transformed" into a sullen, nasty and sarcastic joker who takes great pleasure in making Hare's life utterly miserable. Guu can also swallow anything, and regurgitate it whole. Guu also seems to have various magic powers, which lead Hare to consider her a demon of some sort, but he can't convince most other people of that.