Guren

Guren (紅蓮) is an Area Guardian of the River of Flame on the seventh floor of the Great Tomb of Nazarick.

Appearance
Guren is an abyssal, hellish slime of enormous size. Its sex is unknown to much if not all of Nazarick, with Pulcinella even believing it to be genderless.

Personality
While guarding Nazarick, Guren prefers to conceal itself and pull unsuspecting opponents into advantageous terrain.

The Emissary of the King Arc
Guren noticed a lone Death Knight traveling along the River of Flame, after stalking the undead for awhile, it lost interest upon realizing the Death Knight was not an enemy.

The Two Leaders Arc
Aura mentions to Albedo and Shalltear that should intruders progress past the sixth floor, they would still need to overcome both Guren on the seventh floor and the entire eighth floor before reaching Ainz.

After Pulcinella delivers a message to Mare from Demiurge, Mare remarks that, should he wish to send a reply, he may need to use Guren as a relay and inquires of Pulcinella the whereabouts of Guren. Pulcinella informs Mare that the last time he saw Guren was when Demiurge wasn't present and that it was lying in ambush around the gate to the sixth floor.

Abilities and Powers
Guren is a level 90 hell slime. As a creature optimized for combat, its fighting ability was easily on par with the Floor Guardians.

While being an Area Guardian of the 7th floor's River of Flame in Nazarick, targets would have been dragged into the quicksand-like lava by Guren’s tentacles. Moreover, doing so would render the targets immobile beneath that area effect as they're left to be attacked by a virtually invisible opponent.

Simply put it this way, Guren was considered to be a far more dangerous opponent than even Demiurge himself who also governs the 7th floor. Because Guren didn't need to breathe, the creature could hide its body in the magma. Defeating Guren with normal methods was nearly impossible to begin with.

Demiurge
As Floor Guardian of the seventh floor, Demiurge is Guren's direct superior.

Trivia

 * In the English publication of the Light Novel, Guren's name was translated as 'Crimson'.
 * Guren is Japanese for 'red lotus'. Guren-jigoku, one of the eight cold hells in Buddhist teachings, causes one's flesh to split from the temperature and form the likeness of a red lotus.