A second-year junior high school student who is very studious and forward-thinking. He is innovative and his brain far exceeds his age. He tends to find solutions to the family's (common) mishaps. Yuzuhiko is far more intelligent than Mikan.
He enjoys playing video games and listening to music. His secret pastime is admiring the fictional idol Marumi Maruno. He collects photos, magazines, and keepsakes related to her. However, he keeps this secret from his family (in fear of ridicule) and his friends (since they prefer other idols aside from Maruno).
He has a love for Mayonnaise, and is very picky about which brand his pennypinching mother buys.
Although he reveres in the fact that his Mother is sweet on him, he hates all the attention she gives him. He prefers to be treated more as an adult, and to not be called "Yuu-chan" anymore.
At school, he does well and gets very good marks, but is often intimidated by his teacher, Miss Hara.
He also has many friends, and is seen as one of the more popular students.
His best friend is Fujino, who shares his interests in books, music, and games. However, Fujino is seen as more of a boke to Yuzuhiko's tsukkomi, by acting very immature and childish. Fujino has a crush on Mikan, which disturbs Yuzuhiko. (He even goes as far as to tell Fujino about Mikan's "disgusting" traits, only to get caught and scolded loudly by Mikan.) His other friends include the timid Nasuo Arai, who at one point shared his love for Marumi Maruno, but then changed his mind; the popular girl Sudou, who makes friends with everyone; and the "unique" Yuri Ishida, whose appearance and weird quirks seem to repel the other classmates, yet attract the attention of Yuzuhiko, Fujino, and Sudou.
He also has a "Fan Club", which was founded by Sayu Kawashima, who has a strong crush on Yuzuhiko. She comes up with many ways to convey her feelings to him, but those plans always get foiled, often by Yuri Ishida. He considers Ishida to be her "rival", even though Ishida shows no interest in Yuzuhiko. At times, she gets into situations where Yuzuhiko "saves" her (by catching her when she falls, or bumps into him), which result in a lovestruck scurry. The other member of the "Fan Club" is her best friend, Yamashita. Yamashita is often the voice of reason or gives her the (much-needed) reality check that that calms Kawashima down.
In one note-worthy moment, after seeing Yuzuhiko's charicature drawing of Kawashima (which turned out terrible), Kawashima gave up her feelings for him, but after Yuzuhiko's apology and explanation that he intended the doodle to be "cute", Kawashima regained her feelings.
Aside from his nickname, Yuzupii, the "Fan Club" refer to him by the code name "Hibari-chan" (Little Skylark). This comes from a mass string of word association. (Tachibana Yuzuhiko [his name]-->Yuzu Miso [a citrus-based condiment]-->Miso [bean paste]-->Misora Hibari [enka singer]-->Hibari [Skylark].