Papa's Assassin.

Ryunosuke's a high school student living with his father, Daniel, who's popular with all the ladies. Ryunosuke doesn't know it, but 14 years ago, Daniel was asked to take care of him by a particular woman. Ryunosuke has a few caring friends and he spends his days filled with fun and happiness. But, he also has a secret that he can't reveal to Daniel...!!

(Source: Renta!)