Mizuki Shiiba (椎葉 水樹, Shiiba Mizuki) is Akihiko Usami's cousin from his father's side of the family.
Mizuki returned from America to visit Akihiko and invited himself to freeload in his apartment, to Akihiko's dismay. While he is very attached to Akihiko, he comes off as quite cold to Misaki, which is later revealed to be a result of his feelings for Kaoruko Usami and jealousy of Kaoruko's feelings for Misaki.
|Junjou Romantica characters|
Eri Aikawa • Ryuuichiro Isaka • Kaoru Asahina • Kyo Ijuuin • Ryou Shizukuishi • Haruhiko Usami • Kaoruko Usami • Fuyuhiko Usami • Mizuki Shiiba • Tanaka • Takahiro Takahashi • Keiichi Sumi • Shinosuke Todo • Risako Takatsuki • Tsumori