Kai Tamaru is a 17-year-old high school classmate of Ichika Arima. He possesses long, unkempt black hair, green eyes, and a slender build. His standard outfit is the school uniform: a blue blazer, gray sweater, red tie, brown pants, and formal shoes. Kai maintains a quiet and reserved demeanor, often seeming indifferent to social chatter among peers. A stray volleyball thrown by Ichika struck him during a distracted moment in physical education class, leading to her apology and classmates' laughter. This marked their first significant interaction. His development centers on a growing attachment to Ichika. After school, she noticed him reading "Forward World," a manga series she also enjoys. He offered to lend her later volumes since she only owned the first three. During this exchange, he questioned her about her relationship with Rio Amakusa's older brother, having witnessed them hugging at a festival. Ichika clarified it was accidental, prompting him to caution her about the brother's potentially insincere nature. His feelings for Ichika crystallized on Valentine’s Day. When she offered him "giri chocolate" signifying platonic appreciation, he declined. Instead, he expressed a desire for "ninjo chocolate" indicating romantic interest, directly confessed his feelings, and asked her to consider dating him, leaving her flustered and prompting her to reassess her emotions. His interactions occasionally involve Ryo Amakusa, Ichika’s primary suitor. An encounter outside a convenience store revealed underlying tension when Ryo displayed jealousy upon observing their friendly conversation.