Zenitsu
Agatsuma

Zenitsu is a coward with one perfect skill. Awake, he cries, clings to strangers, and begs to go home. Asleep, when the terror finally knocks him out, he becomes one of the fastest swordsmen in the Corps. He mastered exactly one technique, Thunder Breathing's First Form, Thunderclap and Flash, and his old teacher's advice held: one form, polished until nothing else is needed.

His hearing is as sharp as Tanjiro's nose. He can hear a person's character in their heartbeat, which is why his devotion to Nezuko, whom he first met as a demon in a box, is less absurd than it looks. On Mount Natagumo he protected that box with his life, beheading the Son spider demon with a sixfold Thunderclap and Flash while poisoned and half dead.

The Entertainment District arc gave him his best hour: dug out of a collapsed building, he stood back up alongside Inosuke to take Daki's head at the same instant Tanjiro and Tengen took Gyutaro's. By the Hashira Training arc something in him has quietly shifted. The whining is still there, but he trains without being dragged, and the people around him have started to notice the swordsman underneath.