Heisuke Kukuchi is a fourteen-year-old student in the fifth year at the Ninjutsu Academy, serving as the acting chairman of the Gunpowder Committee. His surname is derived from the Kukuchi Shrine in Amagasaki, Hyogo Prefecture, which is dedicated to the deity Susanoo. Known for his honest, kind, and earnest demeanor, Heisuke is a top student with excellent grades and high intelligence. However, he also possesses a spontaneous and natural personality; the original author has certified him as a natural character who is unconcerned with the atmosphere around him and occasionally makes blunt remarks without any malice. This earnest yet sometimes oblivious side is shown in moments such as when he failed to notice that the cost of sweet rice wine had been included in the committee's budget.

Heisuke's most defining characteristic is his profound love for tofu, which has earned him the nickname the Tofu Kid, a moniker he personally dislikes. His devotion to tofu is such that he always carries freeze-dried koya tofu as a snack, and he is well-versed in tofu cuisine, often cooking elaborate tofu dishes for his juniors and classmates. His passion, however, can be overwhelming; his cooking sessions are known as Tofu Hell by his peers because he continues to cook without regard for the eater's exhaustion. In the anime, the reason for his love of tofu is revealed to stem from his childhood, when he followed his father's instructions to train on a mountain while holding tofu. This contrasts with the original manga, where he initially tried to deny his fondness for it at times. His happiness comes from seeing the joyful expressions of those who eat his tofu dishes.

Within the story, Heisuke takes on significant responsibility due to a shortage of sixth-year students, leading him to act as the stand-in president of the Gunpowder Committee, which includes many junior members. He struggles with this role, especially after the arrival of the unhelpful upperclassman Saitou Takamaru, whom he still treats with respect by adding the honorific san since Takamaru is older. Heisuke shares a bond with Hachizaemon Takeya, another fifth-year who similarly serves as a stand-in committee president, and they have bonded over their shared difficulties. He is also good friends with his classmate Kanemon Ohama, with whom he lives starting from a certain episode, though Kanemon has personally experienced Tofu Hell and often tries to distract Heisuke when tofu becomes the topic of conversation.

In terms of abilities, Heisuke excels in academics, once even completing a sixth grader's summer homework assignment by mistake, and is highly literate. His chosen weapon is the suntetsu, a short metal rod with a ring attached to the middle, which he uses for self-defense or to subdue an opponent by striking their vitals. He is believed to be highly skilled in taijutsu or jujutsu, given the nature of his weapon. Over the course of the series, his character has seen development from a stricter portrayal to his established kind and tofu-obsessed personality, which has remained consistent in later seasons.