Atsushi Toushirou is a tantou, or short sword, brought to life as a warrior tasked with protecting history. He was forged by the renowned swordsmith Awataguchi Yoshimitsu, placing him within a large group of swords known as the Toushirou brothers, all of whom share a similar lineage. His physical form is that of a young boy with black hair cut to ear length and gray eyes.

His personality is defined by a notable contrast between youthful enthusiasm and a surprisingly decisive nature. While he often displays the energetic and somewhat boyish tendencies expected of his youthful appearance, he also holds the position of an elder brother figure among the many Toushirou tantou. This role means that when a situation demands a clear decision or firm resolve, he can set aside his childish side and act with an adult-like level-headedness and practicality. This straightforwardness is reflected in the very blade he embodies, which is an unusually thick ten millimeters at the spine, designed for piercing armor and practical use in actual battle. He carries a quiet sense of pride regarding his history, as many of his past human masters were renowned military generals.

Within the citadel that serves as the home base for the swords, Atsushi Toushirou is the twenty-sixth sword to be manifested by the master. His primary motivation is to fulfill his duty as a sword, fighting to correct the course of history and prove his worth in battle. Despite his small stature, he is determined to show his capabilities directly to his master, referring to them with the title General.

He is deeply connected to his many brothers, particularly the other Awataguchi Toushirou blades such as Yagen Toushirou, Hirano Toushirou, and Maeda Toushirou, forming a tight-knit family group within the larger household. His key relationships are centered on this brotherly dynamic, where he acts as a reliable older sibling. In terms of development, his character arc in the story emphasizes the balance between his two natures, showing that his capacity for mature decision-making is an integral part of him, not merely an act he puts on. He is shown to be a reliable comrade who can be both playfully youthful and seriously resolute when the situation calls for it. His notable ability stems from his historical design as a practical, armor-piercing blade, suggesting a fighting style that is direct and powerful despite his smaller form.