"Lord of Darkness" Guy Crimson「"暗黒皇帝" ギィ・クリムゾン, "Ankoku Kōtei" Gi Kurimuzon」is the oldest of Demon Lords. The Lord of the Palace of White Ice, he has forever ruled over this frozen continent. Being androgynous, he can become a man or a woman at will.
Guy Crimson is referred to using masculine pronouns regardless of his current gender.
Although he normally looks down on strangers, he spares no effort or expense for those whom he knows personally.
Guy Crimson appears to be very forward in his relationships. He made several suggestive and openly sexual advances to Leon Cromwell while in his male form, despite Leon's insistence that he preferred women. Guy responded by on multiple occasions with offers to transform into a woman, only to be rebuffed.
It is stated that transferring from one gender to another is so easy for him that the concept of gender being relevant is alien. He has been known to forget which gender he is using at certain times, but the change in appearance is so minimal no one notices.
Thanks to Rimuru's hospitality when he visited Tempest, Guy developed a fondness for cake and requested for his subordinates to learn how to make them.
Guy's also quite cautious regarding those he deems that can be a threat to him.
A beauty with deep crimson eyes which overshadow the beauty of stars, hair flowing like fire, with a deeper red than the color of blood. He is also of the same height as Leon. While Leon is as beautiful as a woman, Guy's beauty is more neutral. He could be called a woman or man; a bizarre physique.
He exposes a lot of skin while wearing a kimono.
In this form, he is a fiercely beautiful woman, with the same long scarlet hair that flows divinely, and abundant breasts and round buttocks that are really emphasized due to his (her) incredibly slender waist that looks like it can easily break.
Guy says that his male form is optimized for combat while his female form is optimized for high speed thought and calculation processing.
Guy granted the wish of his powerless summoner and destroyed an enemy nation. As payment, he destroyed the summoner's country. And with this, though it was unnecessary, he noticed his awakening as a True Demon Lord. The two Arch Demons he summoned to destroy the first country evolved into Demon Nobles after destroying the latter one. Then, he permitted them to continue serving him.
Milim awakened as a True Demon Lord at the same time as Guy. Her pet dragon was killed by some country. In her anger, Milim destroyed the country and awakened as a True Demon Lord. Unconsciously, she fought with Guy. That battle continued for seven days and seven nights, transforming the bountiful lands in the west into a wasteland.
Eventually, the battle concluded. Milim regained her consciousness and the battle ended. The one who returned her sanity was Ramiris. In the process, the Ruler of Spirits Ramiris absorbed the evil magic of demons and the powerful aura of dragons and began to change. But, she was able to stop Milim's rampage. And the three settled this dispute.
These three were the first Demon Lords. They decided that each of the three would be different than the other two. One would pursue the Ultimate Skill. One would live as one, please. One would judge the world. Because their objectives were different, they could recognize each other.
At some point, Guy Crimson was a member of the Progenitors (Primordials) a group of seven very powerful demons who identified with a color. Guy's color was Red/Rouge. He was summoned as a demon to destroy a country by a weakwilled human to destroy an opposing country. He carried out the summons contract but also chose to destroy the country of the one who summoned him. Due to the numbers killed, he satisfied the requirements to become a True Demon Lord. He eventually became aware of the strongest being there was by the name of Veldanava. He challenged him and lost handily. Veldanava took a liking to him and gave him a purpose, to challenge mankind.
- In the Light Novel version, his male appearance is handsome and masculine while in Web Novel his appearance is a beautiful neutral.
- Although being considered as a Special S rank, his racial evolution was never stated. Therefore, him being a Demon God remains unconfirmed.
- At one point Guy Crimson was a member of the Progenitors known as Rouge or Red.