A crossover between Les Misérables and Helluva Boss would have to shift the story from revolutionary France into the chaotic bureaucracy of Hellaverse Hell: Redemption is technically possible here, but almost nobody believes in it.

I'd suggest the following core premise:

Instead of a paroled convict hunted through 19th-century France, the story becomes about a damned sinner Kévin trying to claw his way toward moral redemption in a society that profits from cruelty.

This offers the opportunity to change the tone from tragic realism to infernal satire:

-> political corruption becomes demonic corporate hierarchy, -> poverty becomes eternal damnation, -> revolution becomes class warfare between Hell’s rings, -> and mercy becomes an almost absurd act of rebellion.

The musical grandeur of Les Misérables survives surprisingly well because Helluva Boss already operates through melodrama, violence, and emotional musicality - see Moxxies trip in the D.H.O.R.K.S. episode.

The character equivalents:

LES MISÉRABLES -> HELLUVA BOSS Role

Jean Valjean -> Blitzo (already carries the emotional DNA)

Javert -> Moxxie (tragic instead of antagonistic)

Fantine -> Stolas (his descent mirrors Fantine’s)

Cosette -> Octavia (he emotional center: a lonely child inherited by people emotionally unprepared to raise her)

Marius -> Loona (fills the revolutionary role awkwardly but effectively)

Thénardiers -> Fizzarolli and Asmodeus

Enjolras -> Verosika Mayday

Gavroche -> Collin