Lilith & Lilim

Level: 55

HP: 6500

Area: Succubus Village

Trivia:
Lilith & Lilim, being succubi, their names may originate from The mythogical creatures, Lilith and Lilin, also known as Lilim.

They're the only one-time appearance boss in the game which manages to actually contribute to the overall plot, revealing Luka's relation to Heinrich as well as making note that the Angel Halo belonged to Heinrich at one point.