A medical action manga that began serialization in Weekly Shonen Jump in January 2026, Under Doctor follows Haiji Kino, a young physician with a unique and dangerous gift. By focusing his concentration, Haiji can see the human body's weak points, injuries, and diseases as visible light. This ability allows him to diagnose and treat critical conditions with seemingly supernatural precision. However, this power is a double-edged sword, as it is the same skill set used by assassins. Raised by his father to be a lethal fighter, Haiji rejected that path, choosing instead to dedicate his life to saving others and mastering medicine.

The story begins in medias res on a commercial airplane. When a passenger falls gravely ill, Haiji steps in and performs a flawless diagnosis that stuns even a renowned medical professor on board. Peace is shattered when armed hijackers take over the plane, and a passenger is shot. Forced into a confrontation, Haiji reveals his secret. His bespoke suit is bulletproof, and his fighting style is brutally efficient; he uses his ability to see pressure points not to kill, but to incapacitate opponents with rapid strikes. After single-handedly subduing the hijackers, Haiji escapes by parachuting from the plane to avoid police questioning, establishing his status as a rogue operator who works outside the law.

The central conflict stems from Haiji's dual identity as a savior and a weapon. He operates in the shadowy world between legitimate medicine and criminal violence, known as the legend of the underworld. His manager, Chiwako Oshimori, helps facilitate his underground practice. Early narrative arcs see him dealing with threats from organized crime, including a confrontation with the Chinese mafia boss Konrenga, who demands Haiji harvest a child's heart for a transplant. Haiji refuses and defeats the boss's men, only to be targeted by a professional hitman named Maxell. Other arcs involve treating a kabuki master with a critical illness and navigating a case where a young patient dies despite a successful surgery, showcasing the grim stakes of his work. The narrative also introduces figures from the legitimate world, such as police officer Jun Kikuta, who becomes indebted to Haiji after being saved and treated, and Professor Makoto Ishiguro, who witnesses Haiji's skills on the plane. As a newly serialized work, the series continues to explore its core theme: a man who possesses the ultimate power to kill, but who fights his own nature every day to be the greatest doctor.