城島 伸一

He is the protagonist's toxic friend #1 and a cousin to Shinobu.

He is tall and good-looking, and so quite popular, but... he "wants to be everyone's Shin'ichi," thus won't get any girlfriend in particular.

Anyway, he has a playboy mentality and seems to quite seriously hold the idea that "all fine girls are mine." He too fell in love at first sight with Aoi who had transferred. He persistently professes his love to her over and over again.

He is quite skilled and able to perform any task you throw at him. He is a narcissist who is quite obsessed with living stylishly.

Her cousin Shinobu is actually the only one he wants to protect. In fact, the reason why he goes this far to act cool is due to him wanting to show off to her.