Wild Heroes.

Segawa Kiichi, a former delinquent, happens to encounter a lonely 10-year-old girl who looks like she is going to be killed by the Yakuza. He saves her by reflex and later realizes that she lost her memory. She doesn't know why the Yakuza are after her and Kiichi is attacked time and again because of that. With his own life in sudden danger, he calls on six friends from his high school days as a delinquent. These enthusiastic, single-minded men band together to protect her to the end.