Jinbei Tsukishima is a sixteen-year-old boy who serves as a constable of the Mushibugyo, an organization in Edo dedicated to hunting giant insects that threaten the city. He is from a偏远 village in津轻, where his father, Genjuurou Tsukishima, ran a swordsmanship dojo. His mother, Kanae, is deceased. A pivotal event from his childhood drives him: while playing with a lord’s son, an incident occurred that embarrassed the lord’s family. The lord blamed Jinbei and sentence him to jail, but his father took responsibility by severing the ligaments in his own foot, thus crippling himself to protect his son. Jinbei carries deep guilt over his father’s sacrifice. To restore his family’s honor and make his father proud, he leaves home to join the Mushibugyo in his father's place.

Jinbei has a carefree, hot-blooded, and optimistic personality. He is always eager for a fight and faces challenges with relentless determination, a trait that defines him as someone who refuses to give up, especially when protecting innocent people or his friends. He is honest, passionate, and shows great trust toward others, even those who seem to be enemies. His courage and kindness earn the affection of several women, including Oharu, Hibachi, and Kuroageha, though he is largely oblivious to their feelings. Despite his bravery, he shares a trait with his father in becoming flustered around women with large busts. He is known for being a morning person who begins his intense training regimen before sunrise. While his straightforward and莽撞 nature sometimes leads others to call him a fool, many also see his spirit as genuine and noble.

Jinbei is a constable who serves on the front lines of the battle against giant bugs. Although he is initially considered the weakest member of the Mushibugyo, he makes up for his lack of experience with sheer willpower and an almost obsessive drive to become stronger. His primary motivation is to protect the people of Edo and to live up to the example set by his father, embodying the belief that one must be willing to sacrifice oneself to protect important people. He looks up to Mugai, the most powerful member of the organization, as an inspiration. Over the course of his journey, Jinbei helps and bonds with each of his colleagues, aiding Hibachi on a mission, convincing others of Shungiku's innocence, and helping Tenma overcome his paralyzing fear of bugs.

Jinbei develops significant relationships with all the main characters. He forms a strong bond with his fellow constables: Hibachi, a ninja with whom he shares a mutual goal of impressing Mugai; Shungiku, a former criminal he believes in when no one else will; and Tenma, whom he helps confront his fears. Mugai is a hero figure for Jinbei, especially after saving his life. He also earns the affection of several women who become integral to his life, including Oharu, the tea shop girl he first saves after arriving in Edo, and the Insect Magistrate Kuroageha, whom he vows to protect and show the clear skies of Edo.

Jinbei’s development is marked by his growth from a raw, impulsive, and relatively weak fighter into a powerful and more reliable swordsman. Despite his lack of skill initially, his iron will and insistence on training allow him to master his family’s techniques quickly. A central part of his development involves a hidden power that resides within him. When pushed to the brink of death, he can enter a berserk state where his hair turns white, he gains animal-like ears, and his physical strength, speed, and durability receive a massive boost. In this state, he becomes a bloodlusting monster that fights on pure instinct, though he initially has no control over it and loses his memory of the event. This power is suspected to be inherited from his parents, connections to the Insect Hunter Clan, and is tied to a strand of the Insect Magistrate's hair.

Despite his small and lean stature, Jinbei possesses superhuman strength that allows him to swing a practice pole weighted with hundreds of kilograms of rock. He fights using the Tsukishima Style of swordsmanship, which his father taught him. Among his techniques are the Mount Fuji Splitter, a powerful downward slash; the Mount Fuji Strike, a devastating blow using the back of the sword's handle; the Mount Fuji Counter; and the Mount Fuji Hammer, a crushing downward strike. He is also able to learn more advanced techniques, eventually mastering the secret Fuji Hammer technique, the Fuji Mountain Storm, and other powerful moves like the Rising Dragon and Meteor. Later in the story, he comes to wield his mother's遗物, the Ame-no-Habakiri sword, a weapon capable of harming the ultimate threat, the Everlasting Insect.