Nahoya Kawata, known by the nickname Smiley, serves as the captain of the Fourth Division of the Tokyo Manji Gang. He is the older twin brother of Souya Kawata, who is known as Angry. Nahoya is of short stature and small build, with fair skin that has a slight tan. He has voluminous curly peach-colored hair, a wide grin that often obscures his eyes, and he wears double silver piercings on his left ear. He is usually seen in the traditional Tokyo Manji Gang uniform, and when not on gang duties, he often matches outfits with his brother by choosing opposite colors.

Nahoya's personality is defined by his constant, unreadable smile, which earned him his nickname. This smile makes him difficult to read during confrontations, adding an element of unpredictability to his fighting style. He is fiercely protective of his younger twin brother, Souya, having vowed to never let him cry. His strongest loyalty is to his brother, though he also demonstrates loyalty to the Tokyo Manji Gang and its members. He enjoys fighting and actively seeks out strong opponents, reflecting a competitive and thrill-seeking nature. Despite his cheerful demeanor, he can be cold-blooded and ruthless in battle, often described as a demon behind the smile.

His primary motivation is the protection of Souya. This bond drives many of his actions throughout the series. He is also motivated by a desire for combat and strength, but he learns to balance this with his responsibility to protect his brother.

Nahoya first appeared during the conflict with Moebius, arriving with the rest of Toman to defend Mikey and Draken. He participated in the brawl and stood with Toman in victory. He has been present in most of Toman's major conflicts, including the Valhalla arc, the Black Dragons arc, and the Tenjiku arc. In the Tenjiku arc, his resolve is tested further as he grapples with gang loyalties and the implications of violence within the gang culture. His growth is particularly highlighted through his evolving relationship with Souya, where he continues to balance his own desire for combat with the need to protect his brother.

His most significant relationship is with his twin brother, Souya Kawata, also known as Angry. This sibling relationship influences much of Nahoya's actions throughout the series. Before joining Toman, the Kawata twins led the Twin Devils Gang, which was based in Meguro and often clashed with Kanji Mochizuki's Jugem gang. The Twin Devils Gang was disbanded before both brothers joined the Tokyo Manji Gang, where Nahoya became the Fourth Division captain and Souya became its vice-captain. He also shows camaraderie with other Toman members, particularly within the Fourth Division, where mutual respect and loyalty are key. He respects Mikey as the leader of Toman and gives him his loyalty.

Nahoya possesses exceptional combat skills, making him a formidable fighter. He is proficient in hand-to-hand combat, using a combination of agility and ferocity. His fighting style is aggressive and unorthodox, allowing him to catch opponents off guard. He relies on his mental fortitude and tactical skills during confrontations. His constant grin adds to his effectiveness by making his intentions unreadable. In contrast to his brother Angry, who has a calm and pacifist nature despite his angry expression, Nahoya loves getting into fights and is a veteran of many gang battles. Despite his strength, he exhibits moments of vulnerability when his emotions, particularly regarding Souya, come into play.