Itazuraguma no GloomySeries

Gloomy, an abandoned little bear, is rescued by Pitty (the little boy). At first, he is cute and cuddly, but becomes wilder as he grows up. Since bears do not become attached to people like dogs by nature, Gloomy attacks Pitty even though he is the owner. So Gloomy has blood on him from biting and/or scratching Pitty. (Source: Cube Works)