Proto-Daimon

Though it hijacked the body of a human boy, the creature held a wholly monstrous shape rather than a human one. The manga and Crystal takes on such beings picture the Proto-Daimons as hulking, worm-like things crowned with skull-like faces.

Sworn to the Death Busters, the monster is driven by a single goal, to strike down Haruka Tenou.

The Daimon shows up in a recollection of Haruka's past, having taken hold of a living boy. It sets upon Haruka, only for Sailor Neptune to fend it off and then finish it with Deep Submerge, after which the possessed boy comes through alive. Nothing on screen ever labels it a Daimon, but its close likeness to the manga's monsters and its choice of a living host rather than an object make the identification safe. Notably, Neptune's Deep Submerge behaved unlike its usual self here, healing the victim much as one of Sailor Moon's own attacks would, the only time a stock move other than Sailor Moon's is shown restoring a human. The beast is never named in the story itself, yet the closing credits list it as Proto-Daimon, the term Japanese publications use for it.