Youji Sagan

He is the sacrifice of the male Zero pair. He is the more cruel and brutal of the two; however, they are both rather blunt and cold toward others. A good example of this is in volume 5, when Ritsuka rushes home after curfew, and Soubi remarks that Ritsuka will probably get a "beating." Natsuo and Youji are both amused by this, and say, "A mother abusing her child! That's the best!" while grinning happily.

Nagisa is unashamedly biased toward Youji, often ignoring Natsuo. According to Youji, this is because he bears a significant resemblance to Nagisa's younger sister.

(Source: Wikipedia)