He is a young man with long straight hair that reaches his waist. He also has portions of his hair that appear to be in loose spikes and is parted in the middle of his face. The color of his hairs left side is lilac and the right side is white. His eyes' color is greyish. He also wears earrings on both of his ears. He is seen wearing a long white coat with black pants. His coat has a sparkly or galactic design on the interior.
He appears to be kind to his customers at the Sky Casino, given the fact that he gave a customer another chance by saying that the game is invalid. 
He also appears to have a strong sense of ownership. In a conversation with Teruko Okura to close the casino, Sigma refuses and even asks her who will reimburse the revenue and reputation if the casino were to be closed and claims that the casino is his life and his customers are valuable to him.
He acts confident and composed even at times of crisis in front of his staff, giving the impression that he's the perfect casino manager and a capable leader. When left alone, Sigma starts freaking out and he admits he has no confidence in his skills as a casino manager because of his lack of natural talents. 
Because he has no memories, no family, and no friends, Sigma's greatest wish is a reason to live. He was also described as implacable by Fyodor Dostoevsky since Sigma is a desperate man.
His ability allows him to exchange information with anyone he touches. The exchange consists of "giving" the personal information they want to know and thus giving Sigma the information he wants to know.
- Leadership skills - As the manager of Sky Casino, he is able to delegate and order tasks properly among his subordinates including taking care of their ccustomers. 
- Memorization - Sigma can memorize the names of traits of his customers, even up to 20, 000 guests. However, it is revealed that he memorize the knowledge of the Sky Casino and his guests since he didn't want to lose his casino. 
Sigma himself was a person born from being written into the Book. When he first opened his eyes and became aware of his surroundings, the first thing that greeted him was not a midwife or a mother but a vast desert filled with nothingness, and his only possession were the clothes on his back and a train ticket from a station that does not exist.
Confused with his circumstances, he wandered around the desert nothingness until he was eventually captured by an armed group and held prisoner, where he eventually unlocked his Gift, causing his captors to then take advantage of his ability for their gain during his time with them. Eventually, he managed to escape from then and continued to wander the world nihilistically due to not knowing his reason for living or existing.
At one point, Sigma was approached and invited by Fyodor to join the Decay of Angels. Upon agreeing, he was eventually given the duty of overseeing the Sky Casino, a job he came to love due to it giving him a sense of purpose. Somewhere along his time together with the Decay of Angels, he eventually obtained information on the location of the "page" of the Book after meeting and attacking Special Division for Unusual Powers director Santōka Taneda using his ability, though he claims that his attack was a mere threat and that he had no intentions of harming him.
|Are you prepared to handle the spoilers ahead?|
In the operation of Hunting Dogs in finding Lucy Maud Montgomery, Teruko leads a team towards the Sky Casino stating that Lucy and the others entered the casino, telling him there is a need to blockade the casino and deploy the police to every section. However, Sigma refuses to close the casino. After someone blew the exits of the casino, Sigma orders the soldiers to not panic and gives them personal orders.
While monitoring the events in the casino, he finds Michizō Tachihara in a hotel room where the RDG1800 counterfeit coins are kept in a safe. Panicking, he decides to make it explode in order to kill Tachihara, but he manages to stop the metal piece and prevent himself from the blast using his ability. After realizing he did not successfully kill him, Sigma decides to use his trump card, an aircraft to attack Tachihara. However, before reaching Tachihara, Teruko manages to stop it on time.
After Teruko's fight with the guards, Sigma orders the customers via their respective room's televisions to attack Teruko and Tachihara on sight and tells them that whoever manages to kill them will have their debts to the casino written off, promising to grant $10,000 to those who can knock them unconscious and $1,000,000 to those who can kill them. After managing to escape the customers, Teruko meets up with Sigma in the telecommunication room.
Sigma then faces Teruko and says that he can not and would not surrender and tells that even the key breaks it would be meaningless unless someone can override the controls with the key, they cannot block the detonation signal. Sigma then throws the key to Teruko. After giving it to her, Sigma attacks her with the Painless Gun, a weapon with a 7.62 mm ammo that can pierce even armored vehicles. However, Teruko manages to stop it and blocks its passage with knives.
Sigma then decides to add a new turret to the device, but Teruko stops him and hints that Sigma is done over. However, Sigma pulls out a directional resonance gun, pushes her onto the floor, and shoots her. After shooting her, Sigma shouts that those are the strength of his feelings. However, Teruko manages to stand up and push Sigma at the edge of the casino.
Teruko then offers Sigma two choices, surrender or else she'll drop him, Sigma again refuses and tells that he had no chance of winning and at that rate, both he and the casino will be destroyed. He then decides to drag Teruko along with him in order to save the casino. While falling, Sigma tightly holds onto Teruko's arms in order for her not to escape, but Teruko kicks him and manages to free from Sigma.
As Sigma is falling, Atsushi Nakajima grabs him and they manage to land at the box with the electric power installation at the casino's base level. Sigma asks Atsushi the reason for saving him. Atsushi replies that he saved him in order to save the Armed Detective Agency since he knows the location of the page. Sigma then asks Atsushi if he is sure he will tell him up front.
Ango Sakaguchi communicates with him through Atsushi's phone, telling him that he'd be able to read the memories of "the page". Sigma then states that he had taken measures against Ango's ability. Ango then replies that they just have to take it the old-fashioned way, torturing the subject until they speak since he cannot forgive the man who stabbed Taneda. Sigma then replies that he did not wish to stab the chief, it was only a threat and gives them the permission to ask him and states that after all, he did not understand what he was born for in the first place.
After the conversation, Nathaniel Hawthorne appears before them. Ango warns Atsushi to be careful with him since he intends to kill him and save Sigma, however, Nathaniel attacks Sigma causing him to fall. Sigma was saved by Atsushi. While grabbing on a pipe, Nathaniel shoots Atsushi on the forehead causing them to fall again, however, Atsushi barely saves himself and Sigma by using his tail as a rope. Sigma then orders Atsushi to let go of his hand or he will die too. Atsushi then shouts that he cannot let die someone whose last words is "I never understood what I was born for". Sigma then lets go of Atsushi's hand.
Sigma is seen falling and sees Nikolai Gogol waiting at the ground for him. After landing, Sigma wakes up at the sight of Gogol. Gogol then explains how he rescued him. Sigma then asks Gogol that if the one who gave instruction to shoot him was Fyodor, what is the reason for rescuing him and states that Gogol should have died during the hostage operation, Sigma asks Gogol how he survived and Gogol proceeds to tell him. Sigma then states that the one he is surprised with is the fact the Gogol is expected to die yet he does not. Gogol then replies that Fyodor is the one who understood him but if they were to use Sigma's ability to read Fyodor's ability, they will be free from "brainwashing".
- "In the superhuman group the Decay of Angels, I'm the man with the least combat-oriented ability. I'm an average person who has nothing but this casino. […] [But] if it's for this casino… I'll do anything."
- "Hey, somebody, tell me. Can't an ordinary man be forgiven for wanting to protect what's important to him?"
- (To Teruko Okura) "I'm certainly just what I seem. I'm this type of man. Empathized by nobody in this world… In sleep and in vigil, I was all alone. That kind of 'me' protecting his home? It's laughable. Even so… My body can't stop itself from moving."
- (To Atsushi Nakajima) "Honestly, I envy those eyes of yours. Anything you consider with such strong eyes is something I could never do. Ask me anything… I'm tired already. After all, till the very end, I never understood what I was born for…"
- (To Atsushi Nakajima) "You are kind… But it's okay. I only did what an ordinary man could."
- Bungo Stray Dogs Manga: Chapter 75.
- Bungo Stray Dogs Manga: Volume 18.
- Bungo Stray Dogs Manga: Chapter 72.
- Bungo Stray Dogs Manga: Chapter 73.
- Bungo Stray Dogs Manga: Volume 18.
- Bungo Stray Dogs Manga: Chapter 76.
- Bungo Stray Dogs Manga: Chapter 72.
- Bungo Stray Dogs Manga: Chapter 74.
- Bungo Stray Dogs Manga: Chapter 78.