Kazuki is quite innocent and gullible. When Risa's friend came to Ikebe, he easily believed all of the stories they told him. He's very shy about his feelings for Risa, but is determined to win her heart.
Kohori, much like Ōtani, is very short though he is 1cm or 0.5" taller than Ōtani is.
Ai-san is a call girl that was hired by Risa's grandfather to seduce Ōtani. Risa's grandfather pointed towards a crowd of people that included both Ōtani and Kohori saying "the shrimp over there", and Ai-san mixed Ōtani up with Kohori. She seduced Kohori and he spoiled her with lavish gifts, including an expensive necklace. After finding out that Kohori was not her target, Ai-san moved on.
★Seiko Kotobuki (Previous)
★Risa Koizumi (Previous)
Risa soon discovers that he is also an avid Umibōzu fan. He very soon develops feelings for Risa, who admits to herself that she finds him 'cute'. Against her better judgment, Risa attends an Umibouzu concert with Kohori which leads to her temporary breakup with Otani.
Kazuki never got along with Otani. Once he learned that Otani was Risa's boyfriend, Kazuki declared that he was going to win Risa from Otani. Likewise, Otani became jealous of Risa hanging out with Kazuki and promised to beat him up if he caught Risa with him.