Ai Ga Aru Kara Osu! summary:

Touma, the next in line to succeed as the head of the Hyuga Group, spends his days beating up street punks and chasing after pretty women. However, everything changes when his father, the head of the group, assigns him a new bodyguard. His bodyguard proclaims: "I am ready to sacrifice my everything for you no matter what the cost," yet what is he hiding from the young master?