Kyo Ethnina

Kyo Ethnina (キョウ＝エスニナ), also known as the Book Hero (本の勇者), is one of the Vassal Wielders from Glass' World.

Appearance
Kyo has white hair with a silvery sheen. His eyes are described as stagnant and rotten, comparing them to the eyes of a dead fish. There is an air around him that is dark and gloomy.

He wears a long coat while wearing a strange belt around his chest, which are 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.

Personality
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.

He's 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 refused to take in any woman whom he considers used goods, such as Albert's and Trash #2's harem. Like a normal gamer, he calls the Waves an update.

Abilities
He was a genius, able to study, control and go around many phenomena, including the summoning of an artificial Wave of Catastrophe, control Spirit Tortoise's power, etc.

He held the Vassal Book against its will and was well versed in using its power. However, since his vassal weapon opposes him, he wasn't able to use all of his powers and even after implementing many more power up methods than the other heroes, the true chosen heroes were still able to fight against him.

Background
He was mentioned to have traveled 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 that anyone wanders inside will be lost unless he wants them to find a way.

From his way of speaking, Kyo seems to have been one of the minority of vassal heroes summed to Glass' world rather than a native. It is also implied that he was like other summoned heroes who thought he was playing a game and not accepting reality.

Volume 7
Kyo was later discovered to be the true mastermind over the Spirit Tortoise incident. He was also the reason for the disappearance of Ren, Motoyasu, and Itsuki. Kyo exploited the three heroes to gain more Spirit Tortoise energy while in the process giving the Spirit Tortoise more power.

He is discovered inside of the Spirit Tortoise at the very core. The Spirit Tortoise's core is destroyed by Naofumi, and Kyo retreated to his world along with the Spirit Tortoise's energy.

Volume 8
He manages to split Naofumi and Rishia away from his party, trapping them in an inescapable labyrinth.

Relationships
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.
 * Vassal Weapon Holders
 * Rishia Ivyred

Trivia

 * Up to the moment of his death, Kyo managed to be the hero who implemented the major number of seven power-ups.