Black Flame-Thunder

Black Flame-Thunder (黒炎雷) is an Intrinsic Skill that Rimuru acquired after evolving into a Demon Slime.

Abilities
It merges the effects of the Extra Skills Black Flame and Black Thunder.

Trivia

 * Before the anime adaptation debuting this skill, in That Time I Got Reincarnated as a Slime: Isekai Memories during the 1st Anniversary opening animation, Rimuru uses this skill against Izis.