Sora Yori Takaku (Miyashita Akira)

When the Devil King announces his retirement, he calls forth his two sons, Yomi and Sora, to give them each a quest. Whichever of them finds a pure Yamato maiden within a year would inherit the throne of the Devil King, while the other would die. Thus begins Sora's sex-fuelled adventure to find a woman that can satisfy his father… (Sakigake!! Otokojuku Wiki)