Sigma

According to the 5th official guide:
What are your strengths and weaknesses? "My strength is that I'm hardworking, and everything else is my weakness."
What's your motto? "Every common man has his own way of fighting."
What do you want now? "I'd like to have a home to come back to."
What's your reward after a hard day at work? "Someone who pats me on the shoulder and says, 'You're doing great.'"

"I'm a member of Decay of the Angel, a group of superhumans, but I have no fighting ability of my own. I'm just nobody. Apart from the casino, I have nothing [...] And for that casino... I'm willing to do anything."[5]
"Come on... Someone tell me. Can't a common man protect what's dear to him?"[1]
(To Teruko Okura) "You're right. As you can see... this is all I have. No one sympathizes with me. Day and night, I'm always alone. Me, protecting my 'home'? What a joke. But... I can't stop my own body."[1]
(To Atsushi Nakajima) "Honestly, I envy your eyes. I doubt I'll ever be able to feel anything again with such strong eyes. [...] In the end, I still don't understand why I was born."[7]

Sigma himself was a man born from the Book. When he first opened his eyes and became aware of his surroundings, the first thing he saw was neither a midwife nor a mother, but an endless desert filled with emptiness. His only possessions were the clothes on his back and a train ticket from a nonexistent station.

Unable to comprehend what was happening to him, he wandered the desert until he was captured by an armed group and taken prisoner. There, he eventually revealed his Gift, and his captors began to exploit his abilities for their own purposes. He eventually managed to escape and continued to wander the world in nihilistic melancholy, unsure of why he lived or existed.

At some point, Fyodor approached Sigma and invited him to join Angel's Decay. After Sigma accepted, he was assigned to oversee the Sky Casino. He enjoyed the job because it gave him a sense of importance.[1] Sometime during his time with Angel's Decay, he eventually gained information about the location of the Book's "page" after meeting the director of the Special Abilities Research Unit, Santoka Taneda, and attacking him with his ability, though he claims his attack was merely a threat and that he had no intention of harming him.[7]

Main article: Information exchange capacity
His ability allows him to exchange information with anyone he touches. The exchange consists of him "giving away" personal information they want to know, and thus receiving information from Sigma that he wants to know.[6]
Skills
Leadership skills: As the manager of Sky Casino, he knows how to properly distribute tasks among subordinates and ensure that they take care of the customers.[5]
Memory: Sigma can remember the names and characteristics of his customers, even if there were 20,000 of them. However, it is revealed that he remembers information about Sky Casino and its guests because he does not want to lose his casino.[5]

Sigma's determination to protect the Sky Casino
So I gave myself a name. Sigma. Casino Man. And finally, I found a place I can call home. My family protects me.
Sigma is a former member of Decay of the Angel and the general manager of Sky Casino.
Sigma is a young man with long, straight hair that reaches his waist. Some of his hair is pulled back into loose buns, and parted in the middle of his face. The left side of his hair is lilac, and the right is white. He has grayish eyes and earrings in both ears. He wears a long white coat and black pants. The inside of the coat has a glittery or galactic pattern. He is 177 cm tall.
He seems to treat his customers well at Sky Casino, considering the fact that he gave the customer another chance after telling him the game was void.

He also has a strong sense of ownership. When talking to Teruko Okura about closing the casino, Sigma refuses and even asks who will compensate for the losses and restore the casino's reputation if it closes. He claims the casino is his life, and his customers are priceless.[3]
He maintains a confident and collected demeanor even in crisis situations in the presence of his employees, creating the impression of an ideal casino manager and capable leader. Left alone, Sigma begins to panic and admits he lacks confidence in his casino management skills due to his lack of natural talent.[5]

Since Sigma has no memories, no family, and no friends, his deepest desire is to find meaning in life. Fyodor Dostoevsky also described him as relentless, as Sigma is a desperate man.[1]