Nishikata is a middle school student seated next to Takagi in class, possessing black hair, thin eyebrows, and small pupils. His standard school attire features a white button-down shirt over a plain white-green t-shirt, navy blue pants, and white shoes with red soles; in winter, he switches to a black button-down shirt with yellow buttons and black pants. As an adult, he maintains a muscular build from a long-term push-up regimen, works as a physical education teacher, keeps his hair shorter and neatly trimmed, and favors casual wear like t-shirts and sweatpants. His daughter Chi physically resembles Takagi but inherits his personality traits.

Easily flustered, Nishikata reacts strongly to teasing, especially from Takagi. Determined to retaliate, his plans consistently fail due to her anticipation. He imposes a strict push-up routine (10 per tease in the manga, 3 in the anime) as both motivation and self-punishment for losing. Despite his competitive drive, he is fundamentally kind and considerate, prioritizing Takagi's well-being over revenge and avoiding actions that could hurt her feelings or dignity, like teasing her when vulnerable. He harbors unacknowledged romantic feelings for her, often misinterpreting her actions as mere teasing.

Their history starts on the first day of middle school when Nishikata returns a lost handkerchief to the lost and found, making him late. The handkerchief belonged to Takagi, who became his seatmate. She correctly guessed the reason for his lateness during their initial challenge, establishing her pattern of outwitting him. Unbeknownst to both, they had an earlier connection: Nishikata frequently played an arcade game under a different username, holding high scores until surpassed by "TKG" (later revealed as Takagi). He repeatedly failed to reclaim the top spot before the game's removal, marking their first indirect encounter.

Throughout middle school, Nishikata frequently challenges Takagi and nearly always loses. He occasionally comes close to making her blush but fails to recognize these moments due to his own embarrassment or overthinking. He values their time together, choosing to walk home with her over other activities, and shows concern for her emotional state, comforting her during family disappointments. He remains oblivious to the mutual romantic tension, despite classmates speculating about their relationship.

As an adult, Nishikata marries Takagi and they have a daughter, Chi. He is a dedicated family man but retains his easily flustered nature, particularly when Takagi teases him in front of Chi. His relationship with Chi is affectionate and playful; he teams up with her to outsmart Takagi, though these efforts typically fail. He is deeply attached to Chi, expressing distress at the idea of her not loving him and becoming defensive about her future relationships. His career as a physical education teacher leverages his muscular build, and students view him as cool yet approachable after interacting with his family.

Nishikata's personality persists into adulthood: he remains strategic in planning teasing attempts against Takagi but often overthinks, leading to self-sabotage. He continues to be highly perceptive of Takagi's emotions and maintains strong loyalty and care for his family. His interactions with Chi mirror his own childhood dynamic, as Chi's middle school seatmate frequently teases her, paralleling Takagi's earlier behavior.

Throughout his development from a competitive but naive middle schooler to a confident yet emotionally reactive adult, Nishikata's core traits—determination, kindness, and a tendency to overthink—endure, shaping his roles as a friend, husband, and father.