Guy Crimson

Species: Devil Lord Title(s): Lord of Darkness; True Demon Lord; Red Primordial; Ancient Demon Lord Gender: Possesses the ability to switch between a male or female body at will. Age: 20,000+ Hair Color: Red Eye Color: Red Kind: Inhabitant Status: Alive Country of Residence: Ice Continent Occupations: Demon Lord Disaster Rank: Catastrophe Affiliations: Octagram

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Guy was summoned to the world by a human as an Arch Demon and was tasked with destroying a nation the human was at war with. He followed that up by destroying the human's nation as well. This earned him his name. An unpleasant-sounding name, like the shrieks of the doomed and desperate as he crushed them. After being named he realized that he had awoken as a True Demon Lord.

(Source: Tensei Shitara Slime datta ken Wiki)