Yuuji Kousaka is the younger brother of Tamaki Kousaka and attends school alongside protagonist Takaaki Kouno. He features red spiky hair, brown eyes, a slim build, and a pale complexion, typically dressed in his gakuran uniform or casual hoodies and trousers.

His personality blends carefree charm with outgoing energy and comical perversion, fueling a passionate interest in photography—especially focused on female subjects. This habit routinely triggers confrontations with his sister Tamaki, who retaliates with her infamous forehead-crushing "iron claw" technique. Yuuji openly envies Takaaki’s effortless popularity with female classmates, viewing him as a romantic rival. Additional traits include a keen love of money, earnest romantic aspirations, and relentless unluckiness that makes him a magnet for teasing and mishaps.

Within his friend circle, Yuuji stands as Takaaki’s best friend, engaging in activities like shopping and lighthearted teasing. He frequently delivers comedic boke-style antics, cementing his role as a recurring humor source. Yuuji appears across the franchise’s original series, OVAs (*ToHeart2ad*, *ToHeart2 AD Next*), and the spin-off *To Heart 2: Dungeon Travelers*, maintaining a consistent secondary role without significant narrative development or backstory evolution.