Krebskulm, also known as Klem, is the Demon Lord of the Soul, a fragmented aspect of a defeated Demon God shattered by a divine entity. Sealed within the ancestors of Rem Galleu, this curse passed matrilineally, binding Krebskulm's soul to Rem's lineage. Partially freed during a Demon King revival ceremony, she first manifested as a three-meter-tall entity sporting insectoid features, five red eyes, horns, and wings of light. She then regressed into a primary childlike form resembling a young girl with amethyst eyes, cream-blonde hair, goat-like horns, elf-like ears, and a lizard tail.

In this child form, she displays an innocent, cheerful, and gentle personality, adhering to a "live and let live" philosophy unless directly threatened, though destructive impulses surface when impatient. Amnesia plagues her, erasing most memories of her abilities and history as a Demon Lord. Her magical power is immense, an inexhaustible flowing river, though she initially demonstrates only basic capabilities like empowering other Fallen or unleashing raw magical blasts. Gradually, she regains fragments of knowledge, enabling her to wield spells such as *Thunder Storm* (lightning attacks), *Dimension Blast* (interdimensional piercing), and *Barrier* (defensive magic). Introduced to biscuits and chocolate by Shera L. Greenwood, she develops a fondness for these treats, which often influence her decisions.

Her relationships center on loyalty and dependency. A kiss solidified a master-slave contract with Diablo, magically binding them. Though sealed within Rem's bloodline, Klem forms a deep attachment to Shera, viewing her as a maternal figure. She also inspires unwavering devotion from Edelgard, a Fallen warrior who serves her unconditionally. Witnessing Rem's apparent death triggers Klem's grief and rage, transforming her back into her true Demon Lord form. This restoration returns her full memories and abilities, intensifying her magical power. She then employs advanced spells like *Infinity Detonation* (defense-ignoring attack), *World Halation* (matter-to-heat conversion), and *Cremation Arrow* (inextinguishable flames), alongside physical strength enhanced by magic, such as punching or hurling heavy objects like coffins. Despite this restored power, influenced by Shera's teachings on morality and her own affection for biscuits, she chooses not to exterminate the mortal races. Reviving Rem returns Klem to her child form, though she retains partial awareness of her actions while empowered.

Klem's development involves reconciling her Demon Lord identity with her new existence. She integrates into Diablo's group, often using disguises like hats to conceal her horns and parasol-skirts to hide her tail for societal blending. Her bond with the party deepens, leading her to actively participate in conflicts, such as opposing the Gelmudo Empire's atrocities. While prone to childlike impulsivity, her experiences foster a protective instinct toward her companions, reinforcing her rejection of her original destructive purpose.