Kenji Natsume is portrayed as candid, competitive, and fiercely confident in his basketball abilities. His aggressive and stubborn nature often made it difficult for him to build strong relationships with others, including family members and peers. Upon enrolling at Kuzuryū High, his confrontational behavior put him at odds with both the faculty and the basketball club, nearly resulting in his expulsion. After apologizing for his actions, however, he officially became a member of the team. Over time, Natsume demonstrated significant personal growth, becoming more tolerant and cooperative with those around him.

Despite his fiery personality, Natsume also shows a supportive and caring side. As one of the most experienced players on the team, he frequently offers guidance and advice to his teammates, particularly Yasuhara, whose skills he came to respect. Their mutual recognition eventually developed into a friendly rivalry.

Outside of basketball, Natsume is deeply devoted to his younger sister, Juri, having once promised her that he would become the best high school basketball player. His determination to keep this promise underscores his commitment to both family and the sport.

Natsume’s competitiveness also fuels his drive for improvement. Initially shaken after meeting Fuwa, a player whose talent surpassed his own, he began to question his abilities. This realization prompted him to reassess his mindset, leading to a more disciplined and reflective approach to basketball. As a result, his attitude shift not only strengthened his character but also elevated his performance on the court.

Kenji Natsume stands at approximately 5 ft 10 in (178 cm). He has black eyes and thick, voluminous black hair, which he typically styles in box braids, bantu knots, or occasionally cornrows. When unbraided, his hair has a textured and full appearance.

Natsume has a tattoo on his right arm that reads “Greased Lightning,” which he usually conceals during games by wearing a black sleeve. On the court, he wears the jersey number 11 and favors Nike Air Jordan 13 sneakers.

Kenji Natsume was born in Hiroshima Prefecture and speaks in the local dialect. His early childhood was marked by family difficulties, as his parents divorced when he was young due to his mother’s infidelity. Following the separation, his mother left, and Natsume was raised by his father, a construction worker. Encouraged by his father, Natsume developed a love for basketball at an early age. For his birthday, his father gifted him his first professional basketball, which became one of his most treasured possessions.

Tragedy struck when his father died in a workplace accident. Afterward, Natsume’s mother found the basketball among her late husband’s belongings and gave it to her son. Although she later took him back into her care after remarrying, Natsume harbored deep resentment toward her for the hardships she caused his family. He also clashed frequently with his stepfather, leading him to move to Kanagawa Prefecture to live with his aunt.

Natsume shares a close relationship with his younger sister, Juri, with whom he often speaks on the phone. He once promised her that she would see him compete in the Inter-High Tournament once he entered high school. This vow motivated him to join the Kuzuryū High basketball team as an official member.

During the Monster Bash Tournament, Natsume injured his right knee while attempting a layup against Kikugawa High. He was subsequently taken in by his mentor, Karasawa of Jōnan University, who arranged for rehabilitation under Watase, a training and recovery specialist. Alongside rehabilitation, Natsume committed to strength training to address his physical weaknesses. Although his knee eventually healed, he occasionally still experiences pain during games.

Kenji Natsume is regarded as the ace of Kuzuryū High, possessing a natural talent and deep understanding of basketball. Initially, his pride and individualism made him a selfish player, as he believed personal strength was the key to leading the team. Over time, however, he came to recognize the importance of teamwork, shifting his perspective to strive for victory alongside his teammates rather than alone.

Natsume is left-handed and excels as a scorer, serving as the focal point of Kuzuryū’s offense. Along with Sora Kurumatani, he consistently contributes the majority of the team’s points. While primarily offense-oriented, he is also a capable defender, often tasked with guarding the opposing team’s strongest players. His speed and agility make him effective in transition, and he frequently utilizes the double-clutch technique when finishing layups. In addition to scoring, he occasionally assists in ball distribution, displaying versatility by playing both small forward and shooting guard positions, classifying him as a “swingman.”

During training with Karasawa, captain of the Jōnan University team, Natsume’s potential was highlighted as being capable of reaching the Zone. This state represents the ideal balance between conscious strategy and instinctual play, enabling players to make optimal, split-second decisions. While only professional or highly experienced athletes can typically control entry into the Zone, Karasawa observed that Natsume may achieve it by properly channeling stress into focused energy.

The given name Kenji (健二) is composed of ken (健), meaning “healthy,” “robust,” or “strong,” and ji (二), meaning “two.” His surname, Natsume (夏目), combines natsu (夏), meaning “summer,” and me (目), meaning “eye.” Together, his full name can be interpreted as “strong second son with the eye of summer.”