Fomoire

About
Fomoire was a powerful water elemental Duendy who attacked Shura in the Underworld.

The abundance of jaki in hell combined with Kusunagi Maru's distressed state after being touched by Katsuragi Karin made him impervious to attacks.

Kusunagi Maru got confused by Karin's "human, yet inhuman" Ki and was unable to focus on sucking jaki meaning that Fomoire could not be weakened.

An odd duendy named Cerberus helped out in the nick of time and killed Fomoire.

Trivia

 * His name is based on a supernatural race from Irish mythology
 * Fomorians