The fight between Diablo and Violet in That Time I Got Reincarnated as a Slime is commonly referred to as their light novel / anime-adjacent scene , and the clearest result I found points to Season 4, Episode 14 in fan- uploaded episode references, not an officially confirmed aired anime episode yet.

What I found

  • A fan-posted result labels it as “DIABLO VS WHITE x VIOLET x YELLOW! Slime/Tensura Season 4 Episode 14”.
  • Other results that mention “Diablo vs Violet” are mostly fan edits or short-form clips rather than an official episode listing.

Important note

If you meant another series with characters named Diablo and Violet, one result points to Diablo Guardián, Season 2, Episode 8 titled “Yo Maté A Violetta”.

So, for Tensura , the best match I found is Season 4, Episode 14.