The hero Toto possesses genuine talent and overwhelming physical strength, yet his extreme shyness, particularly around women, has left him stranded in the starting town of Promna, unable to form an adventuring party. His fortunes appear to change when three beautiful women, Ciel, Anemone, and Goa, suddenly invite him to join their party. Overjoyed at finally beginning his long-awaited journey, the socially anxious Toto eagerly accepts, unaware that his new companions are all assassins, each with a secret contract to eliminate him.

The trio of would-be killers consists of Ciel Zebul, the daughter of the Demon King who seeks to prove her independence; Anemone, a professional hitman disguised as a priestess; and Goa Minagawa, an inn manager and poison specialist who refers to herself as "the Manager". Their mission quickly devolves into a comedic rivalry as the three women compete with one another over who can successfully finish off the oblivious hero. Toto's crippling social anxiety manifests physically, causing him to faint whenever he becomes too flustered, such as when a woman links arms with him or invades his personal space.

The narrative unfolds across twelve episodes as the dysfunctional party travels through a fantasy world, with Toto remaining blissfully ignorant of the constant attempts on his life. The series follows a specific episodic structure, with the first half consisting of standalone comedic situations that highlight each character's personality and assassination methods. The latter episodes shift toward more continuous storytelling arcs, focusing on the growing bonds between the three female assassins as they navigate their conflicting loyalties and develop genuine feelings for their target. Despite their deadly intentions, each woman possesses hidden depths: Anemone despises seeing children suffer and secretly dreams of running an orphanage, while Goa yearns for authentic relationships after a lifetime of being feared or served. Toto's own mysterious past, including the large scar on his face and the loss of his family, remains largely unexplored as he continues to serve primarily as a catalyst for the heroines' development rather than experiencing significant personal growth himself.