Mizuki Shiiba

He is Akihiko's twenty-five year old cousin from his father's side of the family. He has returned from America to visit Akihiko, freeloading in his apartment.

[Spoiler] While he is very attached to Akihiko, he comes off as quite cold to Misaki. It turns out that the reason he's so cold to Misaki is that he has feelings for Kaoruko. [/Spoiler]

(Source: Wikipedia)