Ikeno Koi manga
The story is about a girl who has a vampire father and a werewolf mother. Despite her "Addams Family" home life, she just wants to live like a normal girl. Unfortunately, she is "blessed" with the unfortunate power to turn into anything she bites. Example: she accidentally bites a cake the wrong way, and she'll turn into a cake. Mix school yard romance into all that--she has a crush on the cute guy in school, and she has to deal with a prissy love rival without exposing her supernatural powers--and you've got a great manga.
Suzune never got along with her cousin Yuuma when they were kids. Now that she's in high school, though, he suddenly shows up again after years of separation, and he's like a completely different person -- he's become cool and good-looking! Yuuma says that his grandmother told him, "Protect Suzune," and so now he wants to live with her...!?