Takeru Arashiyama is Hotori Arashiyama's younger brother, seven years her junior. He has a younger sister, Yukiko, three years below him. As the middle child, he navigates typical sibling dynamics with both friction and affection. Takeru interacts with Hotori through a blend of tolerance and frustration, her clumsy and overbearing tendencies complicating his daily life. Though generally peaceful, her actions frequently cause him unintended trouble. He occasionally redirects resulting frustrations toward Yukiko, sparking conflicts that require parental intervention. Their mother, Yukimi, often mediates to restore family harmony.

Takeru maintains a calm, ordinary daily demeanor. He dedicates substantial leisure time to video games at home and trading card duels with school friends. These gaming habits draw criticism from classmate Eri Isezaki, nicknamed "Ebi-chan." Eri's tsundere-style crush on him introduces comedic tension, and her unexpected weekend meeting requests disrupt his straightforward routine, adding confusion.

Despite his unassuming nature, Takeru displays perceptive problem-solving. When Yukiko lost her Nintendo DS, he devised a strategy: giving her acorns to play with, predicting she'd scatter them in frequented areas. He anticipated neighbors would complain about the resulting mischief, knowing Hotori's detective-like curiosity would drive her to investigate. This approach revealed Yukiko's movements and recovered the lost item, demonstrating Takeru's strategic thinking and subtle grasp of family dynamics.