Boku to Mimosa no 75-nichi

Shuuto Rindou is the son of Yakuza boss Takeshi Rindou, the brutal and voracious head of the Rindou-gumi. Takeshi is likewise a heartless and abusive parent, but Shuuto finds comfort in the companionship of his new bodyguard, the beautiful and mysterious Mimosa, whom he dubs as his "older sister". Later, Shuuto walks in on his father assaulting Mimosa. Reaching his limit, Shuuto attacks his father, but it's Mimosa who swiftly finishes him off, protecting the young man. The two proceed to go on the run together...
It's the start of a violent story about blood-soaked "family" ties.