Aizawa

相沢

The main antagonist in the series. [Spoiler] It is revealed that Nanami was once with Aizawa, conducting brutal experiments in the laboratory, but met Shinichiro and left him. Aizawa has a son named Kai Nagase, but in the Drama CD's addresses him by "Kai-Kun". In the anime, he manipulates with Sunao's feelings and turns him against Sora Hashiba. [/Spoiler] Source: Wikipedia