Koukin is Hakufu's cousin and housemate. They are rather close with each other. Koukin often tries to save her from doing foolish antics as well as shielding her breasts when they are bouncing or exposed for people ogle at. Koukin and Hakufu do however argue constantly because of the former's cautiousness compared to the latter's recklessness. Hakufu notes that Koukin has seen her in the buff many times that she is only embarrassed when others are similarly seen. Overall, Koukin loves Hakufu and wishes to keep her safe even if it costs his own life. However Hakufu deeply cares about Koukin and also depends on him to carry her on his back whenever she is hurt,tired or sleepy.