Swamp Demon

Blood Demon Art: Body Liquefaction

His Blood Demon Art lets him dissolve into a puddle to infiltrate homes undetected and split himself into multiple semi-independent bodies (all counted as one demon), each retaining part of his strength, until Tanjiro severs his arms and defeats him during his first solo mission.

The Swamp Demon is a pale, blue-haired young man with prominent forehead veins and claw-like nails, able to liquefy his body into a puddle that conceals a vast swamp-like interior space.

The Swamp Demon is predatory and manipulative, luring victims into his puddle form with false hospitality before revealing his true, murderous intent.