The story begins with Task, a young boy living alone after his mother disappeared and his father became distant. One day, his father forcibly takes him to a hospital-like facility, where he undergoes a painful procedure and blacks out. He awakens to find himself in a fiery inferno, bound to a bed, experiencing intense pain as his body is consumed by flames. He realizes he cannot end his own life.
Task, now named Sabu Task, is a 17-year-old student at ESP Academy, a school for those with special abilities. He is an F-rank, considered a "no-ability" and the only one of his kind. He receives a stern email from his teacher, Ken Misaki, a sharp-eyed woman with an eyepatch, about his poor attendance, forcing him to attend a private lesson. Task, despite his F-rank and lack of abilities, possesses a unique double-layered "ability mark" on his right hand, classifying him as a "Secret Child." He is a survivor of the "Lost City," which explains his delayed enrollment.
During his private lesson, Ken Misaki explains the ESP system and Task's unusual mark. She reveals that his inability to use abilities means he cannot participate in practical training, hence his higher number of written assignments. Task expresses his disdain for school and useless knowledge, which provokes Ken Misaki to attack him with a stun gun. She reveals herself to be an ESP specialist trained for combat. After a harsh scolding, she playfully reveals her attack was a joke. Task, still feeling inadequate, jokes about proposing to her, which leads to a comical, aggressive reaction from Ken Misaki. She then resumes her lesson, explaining the academy's structure and the typical age of ability awakening.
The next day, Task begins special training at Ken Misaki's home, a traditional Japanese mansion. He learns combat techniques, mental focus, and reaction enhancement, focusing on close-quarters combat due to his aptitude. After three months of intense training, Task feels a growing confidence, even managing to score points against Ken Misaki. He lives in a small container house due to his F-rank status. He is greeted by Yuu, a cheerful younger neighbor with super-strength abilities, who is a B-rank. Yuu expresses her excitement about Task participating in the upcoming Rank Festival, an annual tournament where students showcase their strength. Task reveals he has been training with Ken Misaki and feels confident.
On the day of the Rank Festival, Task is nervous but physically prepared. Yuu makes him katsudon as a good luck charm. He heads to the tournament hall, where he learns his first opponent is the A-rank "Spatial Walker" Manjou Ouya. Despite his F-rank and lack of abilities, Task enters the arena. He uses his firearms and agility to evade Manjou Ouya's powerful, teleportation-like attacks. Task manages to break Manjou Ouya's weapon and land a blow with a hidden knife, but Manjou Ouya retaliates with a devastating "ultimate technique," severing Task's right arm.
As Task loses consciousness, he recalls Ken Misaki's past as a mercenary and her harrowing experience in a battle against ESPs. He is jolted back to consciousness by Ken Misaki's encouraging shouts, reminding him of her lesson about never giving up. Fueled by her words, Task, despite his severe injuries, manages to defeat Manjou Ouya by tripping him and delivering a final blow. He is promoted to D-rank.
Meanwhile, a hikikomori girl named Kibou Mai is kidnapped by a man in a suit. She wakes up in a dark cargo hold and overhears her captors discussing "n'ESP" and "Tricksters." She manages to escape her restraints and is accidentally sucked out of the ship into the sea, where she is rescued by Task.
Task, recovering from his injuries, takes Mai in. He learns she was kidnapped and is a wealthy heiress. Yuu, initially jealous, eventually accepts Mai's presence. Task is summoned by Ken Misaki, who reveals the kidnapping is linked to the Tricksters, an anti-social organization creating artificial ESPs. Ken Misaki offers Task a position in the Self-Defense Force, which doesn't rely on abilities, but he chooses to continue as an ESP, aiming to win the Rank Festival. He requests a custom weapon from Ken Misaki.
The story concludes with Task, Mai, and Yuu preparing to go to the staff room to meet Ken Misaki. The narrative hints at a larger conspiracy involving "Adam and Eve" and a "Golden Fruit." Task, now with a prosthetic arm, is determined to fight and protect those around him, inspired by Mai's desire to fight for what she wants and Yuu's unwavering support. He has accepted his path as a fighter, even without his original right arm.
