Ken Usato is the main protagonist of his story, an ordinary Japanese high school student who is unexpectedly transported to a fantasy world. Prior to his summoning, he leads a simple and unremarkable life, considering himself a run-of-the-mill student with no outstanding features. He is initially intimidated by his more accomplished classmates, the student council president Suzune Inukami and vice-president Kazuki Ryusen, but a chance encounter on a rainy day leads to a budding friendship between them. Usato was never meant to be a hero; he was simply in the wrong place at the wrong time, getting caught in a summoning spell that was intended only for Suzune and Kazuki.

In terms of personality, Usato displays a somewhat lazy inclination and a tendency to avoid unnecessary effort, believing that magic should simply make life easier. However, this surface-level trait belies a deep-seated competitiveness, obstinacy, and an exceptional determination that emerges when he is truly challenged or motivated. He is often modest and underestimates his own potential, but he possesses a strong sense of wanting to make a difference and lead a more interesting life. When pushed to his limits, he can display a fearsome and terrifying expression that causes even his allies to recoil, earning him nicknames like monster or demon among his peers. Despite these fearsome monikers, he is admired for his courage, creativity, and the unwavering resolve that allows him to survive training that no one else can.

His primary motivation shifts from simply surviving his unexpected predicament to fully embracing the purpose he was given. After discovering his rare aptitude for healing magic, he is forcibly recruited by Rose, the captain of the kingdom's Rescue Squad. Under her brutal and rigorous tutelage, Usato is driven to revolutionize the way healing magic is perceived and used in this new world. His goal becomes to transcend the limitations of a traditional support role, proving that a healer can be just as formidable on the front lines as any warrior. The story follows his growth as he strives to become an irreplaceable asset to the Rescue Squad, protecting others and mastering his unorthodox abilities.

Usato's role in the story is that of an unconventional hero who defies expectations. While his friends Suzune and Kazuki are celebrated as the chosen heroes with powerful offensive magic like lightning and light, Usato is overlooked and considered a mere nobody. However, his journey forms the core of the narrative, as he becomes a central figure in the kingdom's struggle. He is the heart of the Rescue Squad, a unit dedicated to saving lives on the battlefield, and his unorthodox methods and combat prowess make him a crucial asset who garners respect and fear from both allies and enemies alike.

Key relationships heavily define his journey. His bond with his former classmates, Suzune Inukami and Kazuki Ryusen, anchors him to his old life. He forms a particularly significant friendship with Kazuki, who saw him as a true friend after an act of kindness. The most important relationship is with his mentor, Rose, the fearsome leader of the Rescue Squad. She is the one who recognizes his latent potential, subjects him to inhuman training, and teaches him the true, aggressive applications of healing magic. His fellow members of the Rescue Squad see him as a peculiar, powerful, and unpredictable figure, ultimately coming to respect him despite their initial teasing.

Throughout his development, Usato transforms from a passive, average student into a resilient and creative fighter. His survival of Rose's infamous training regimen is a testament to his tenacity, and it forges him into a person with immense physical strength, endurance, and a tolerance for poison. He evolves his thinking to combine healing with combat, changing from someone who merely heals wounds to someone who can actively engage and incapacitate enemies without causing lasting harm. His values begin to mirror his mentor's, and his physical capabilities gradually surpass those of a normal human. This growth is fueled by his creativity and stubbornness, allowing him to devise new magical techniques that leave the entire world in awe.

Usato's notable abilities center on his unique application of healing magic. Unlike conventional healers who stay in the backlines, he uses his power offensively and defensively. His signature technique is Permanent Healing, which involves constantly activating healing magic over his entire body. This allows him to push his physical training to superhuman levels, recover from injuries instantaneously, and even use the healing effect as a defensive barrier or physical reinforcement. He has also developed several original combat techniques. His Healing Fist allows him to land a punch that heals the physical damage of the blow but leaves all the pain and impact, effectively incapacitating an opponent without inflicting lasting injury. He can also create a Healing Projectile, a ball of healing magic that he can throw as a tangible, and surprisingly painful, attack. In desperate situations, he can unleash his forbidden technique, the Explosive Healing Palm, which forces his healing magic to explode at great personal risk, temporarily robbing him of his ability to heal. Through these methods, Usato completely changes the perception of healing magic, turning it from a purely supportive art into a powerful tool for combat and survival.