Kazushi Kine is a male high school student attending the same school as protagonist Natsuo Fujii and is one of Natsuo's close friends. He has brown hair reaching to his neck and gray eyes. Kine displays a consistently lighthearted and carefree demeanor, often contributing a playful or humorous tone to group interactions, leading peers to characterize him informally as a "playboy." He is frequently seen joining Natsuo and their friend Yuya Masaoka in typical school activities and casual conversations.

His dialogue reflects a teasing, joking nature, exemplified by exclamations like "For real?! He's one of those perverted teachers, then!" in reaction to gossip, or lighthearted comments such as "What's this? Hina-chan, you interested in my butt?" He openly expresses admiration for their teacher, Hina Tachibana, using the nickname "Hina-chan" and stating "Isn't Hina-chan great? I wanna go out with her!" Kine voices envy when perceiving preferential treatment toward Natsuo, complaining "Why is Natsuo the only one who gets special treatment? That sucks!" His interactions include prompting Natsuo for opinions with questions like "True or false... Natsuo, which do you think it is?", reacting with exaggerated exclamations such as "Whoa! Whoa!", and readily agreeing to group decisions with phrases like "I'll go! I'll go!" His role remains primarily that of a supporting friend within the school setting, contributing to group dynamics through his established personality traits.