A beauty with deep crimson eyes which overshadows 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 Cromwell. 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.
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.
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.
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.
Guy ventured to the Ice Continent and established his control over the continent. He and Velzard formed a pact with each other and Velzard became a subordinate in addition to the green primordial and blue primordial
He seems to find Rimuru Interesting for both his personality and power (being able to make someone like Diablo his subordinate and that he has an ultimate skill). Guy and Rimuru start off with a neutral relationship with Rimuru being wary of Guy when he is around but they eventually gain a positive relationship when Guy visits Tempest for the first time.