Kyo has white hair with a silvery sheen. His eyes are described as stagnant and rotten, comparable to the eyes of a dead fish. He carries a dark and gloomy aura around him.
He wears a long coat while wearing a strange belt around his chest, which is full of test tubes. He also wears leather gloves and shoes. He is described looking either like a scientist or an alchemist.
After his death, the remnant of his soul takes the appearance of a skinny man in his thirties, completely different from his physical appearance, but his voice is the same.
Kyo fancies himself a genius. A rampant egomaniac, whenever his opponents make mistakes, he will repeatedly call them stupid, yet he makes use of his attacks in extremely simple and easy-to-see-through ways. Also a megalomaniac in his quest for more power, he sees the world as nothing more than a game, its people merely NPCs that exist for his entertainment, and it shows through his frequent use of "Gamer Jargon" such as calling the waves an update, much like how Ren Amaki sees everything around him.
He is also a rampant pervert, as shown by his openly admitting that he intended to brainwash the members of Naofumi's party and add them to his harem of other brainwashed women. But he refused to take in any woman whom he considers as 'used-goods', such as Albert's and Trash 2's harems. In spite of having cheated death many times the idea of a permanent death through being devoured by a Soul Eater or Soul-Eating attribute in a weapon terrifies him to his core.
Some time ago, Kyo died in his old world, but through intervention of an otherworldly power, he was reincarnated into Glass' World. He was mentioned to have travelled around the world, asking people about their troubles and invent a way to solve them. He saves Yomogi along the way.
Long ago, he built his laboratory inside a sealed mansion far away from the capital. It was within a thick fog. Anyone who wanders inside will be lost unless he wants them to get to the mansion.
- Vassal Weapon Holders
- Rishia Ivyred: Rishia considers Kyo to be the person she could never forgive and believes that there was a destiny than it was hers to kill Kyo. Rishia unlocks her hidden potential to fight Kyo which made Naofumi nickname her as a protagonist. Kyo was also easily annoyed by Rishia for her ideals and also for getting on his way. She always managed to spoil his plans on many occasions.
- Albert: Albert was a fellow Vassal Weapon holder who wielded the Vassal Mirror. However, it seems that Kyo only befriended Albert for as long as he was deemed useful. Eventually, Kyo turned on him and used him for one of his twisted experiments.
- Yomogi Emarl: Yomogi is Kyo's childhood friend. Before she attacked the heroes she had a high opinion of Kyo and saw him as a generous adventurer who made the invention to bring joy to the world. However, after stealing the Spirit Tortoise's energy, Kyo used her as a disposable asset. She truly cared for him and tried to correct him when he went off the path. After seeing his true colors, She joined hands with Kizuna to take him out.
- Tsugumi: Tsugumi was part of Trash II's harem who went to Kyo after Trash II was killed. Persuading Tsugumi and her companions to follow him, he used them as living experiments. They were infused with Guardian Beast flesh to become human-guardian beast hybrids and gave them dangerous demonic weapons created from the Spirit Tortoise's energy. After seeing his casual use of their lives, Tsugumi joined the heroes and helped them defeat Kyo.
- Due to him not being a genuinely chosen Hero picked out by the Vassal Book, Kyo was never able to fully use the Book's power to its maximum potential. In fact, the Vassal Book itself despised Kyo and [telepathically] called out to its fellow Vassal Weapons, relaying the message to have their chosen heroes kill him and free itself from his control.