"Hitman from Today" centers on Kenta Usami, a high school student who unexpectedly inherits his late grandfather's role as a professional hitman. The narrative begins with Kenta discovering his grandfather's secret life and the organization he worked for, a shadowy group that handles assassinations for powerful clients. Despite his initial reluctance, Kenta is thrust into this dangerous world, forced to balance his ordinary school life with the deadly responsibilities of his new profession.

The story explores Kenta's struggle to adapt to his dual identity. On one hand, he maintains the facade of a typical teenager, attending classes and interacting with friends. On the other, he must complete high-stakes assassination missions, often involving morally ambiguous targets. The series delves into the psychological toll of this double life, as Kenta grapples with the ethical implications of his actions and the constant threat of exposure.

Key characters include Kenta's mentor, a seasoned hitman who guides him through the intricacies of the profession, and his childhood friend, who remains unaware of his secret life but becomes increasingly suspicious of his erratic behavior. The organization Kenta works for is depicted as a cold, calculating entity, with its own hierarchy and rules, often placing Kenta in situations where he must choose between loyalty and his own moral compass.

The plot is driven by a series of missions, each presenting unique challenges and moral dilemmas. These missions serve as a vehicle for character development, revealing Kenta's growing competence and the internal conflict he faces. The series also introduces rival assassins and external threats, adding layers of tension and complexity to the narrative.

As the story progresses, Kenta's skills as a hitman improve, but so does the danger surrounding him. The line between his two lives begins to blur, leading to moments of intense drama and action. The series maintains a focus on the consequences of Kenta's choices, both for himself and those around him, creating a narrative that is as much about personal growth as it is about the world of professional assassination.