A 39-year-old legendary hitman who has been turned into a child after being stung by a mysterious wasp.
Under orders from the boss of "ZOO", he is forced to enroll in Rikka Middle School. While bewildered by his sudden school life, he gradually discovers the joy of studying. His marksmanship remains top-tier.

The daughter of major corporation Mitsuoka Pharmaceuticals, and a high-achieving honor student skilled both academically and athletically.
She helps run her uncle's ramen shop. Beautiful and admired by many, she's developed a strong dislike for boys due to being confessed to far too often. Due to a particular circumstance, she becomes a target of assassins.

Jūzō's partner in the secret organization "ZOO".
As Jūzō infiltrates the middle school, Kotatsu supports him constantly through an earpiece and camera-equipped glasses. Skilled at cooking, cleaning, and all household tasks, he supports Jūzō's daily life while often being dragged around by him.

A hitman sent to school by the Chinese organization “Yugang” to go after Noren Mitsuoka.
If he loses his pacifier, he becomes extremely anxious and can’t communicate properly.

A second-year student in Rikka Middle School's elite group, the "Unicorn".
He is the ace of the school's soccer, basketball, and baseball teams. With superhuman athletic ability, he is known as the "Super Middle Schooler". He dreams of becoming the top athlete in every major league.

A top-ranking assassin affiliated with the industry’s largest assassination organization, “JARDIN.”
For reasons unknown, he is investigating the secrets of Mitsuoka Pharmaceuticals, just like Jūzō. He specializes in hypnosis.

A top-ranking assassin belonging to the organization “JARDIN,” who carries out missions alongside his older brother Kazuma.
With overwhelming physical abilities, he attacks Jūzō and his allies using golf as his weapon of choice.

A third-year student at Rikka Middle School and the head of the Home Economics Club.
Mature, caring, and dependable, she is affectionately called "Anego (big sis)" by Jūzō.

A brilliant researcher who leads the science division within “ZOO” and Jūzō's ex-wife.
She is working on a way to return the transformed Jūzō to his original adult form.

A 39-year-old legendary hitman who works for the secret organization "ZOO."
Known for flawlessly accomplishing even the most impossible missions, he suddenly finds himself transformed into a middle schooler after being stung by a mysterious wasp during a mission to take down a rival group. He's divorced.