B't X

The Dark! Fear of the Underhell (1x18)

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Kotaro struggles to figure out a way to destroy Raphael. If Raphael keeps metamorphosing, he'll absorb the entire planet! Kotaro has to figure out what exactly Raphael is and keep him from being killed by his jailer in UnderHell! Meanwhile Fou must battle one of the Dark Knights to save Karin!