Echoes in an Empty Frame

In a world where a single brush-stroke can summon cities or drown armies, fifteen-year-old Enō Sumito wields the Living Brush-until he meets the Embodiment of Evil itself, a shapeless void given will. Their final clash ends with a slash of white ink that doesn't kill: it freezes the painter inside a paper-thin prison.
The world forgets his name.
Inside the colorless void Sumito does not age, but every second is white-hot agony; the ink eats at his nerves like acid yet never lets him pass out, a century-long scream no one hears.