Shin is a tall man with a muscular build, short blonde hair, blue eyes, and pale skin. He is often seen in a formal suit while wearing a heart-shaped mask backward. He uses glasses when he isn't wearing his mask. He has stitches running along his arms and hands from his surgery to gain magic powers. He usually uses a claw hammer to fight, which is his primary weapon of choice besides his magic.
Shin has a young-looking face without any facial hair, but with a noticeable forehead, which wasn't very obvious at the beginning of the manga, though it became more prominent with the progress in art style. He also had spiky hair, but especially in later chapters, his hair is closer to a more realistic or at least shorter hairstyle.
As a teenager, Shin used to wear his then very long hair styled in a ponytail. At that time of his life, he didn't yet wear glasses, so it can be assumed that Shin's eyesight has gotten progressively worse with time since then.
Despite his job as En's cleaner, Shin has a very easy-going personality and is rather approachable by all within the En family. He cares deeply for his partner, Noi, and the two share a close bond. Though Shin is seen to be rather modest around Noi, since he is often embarrassed by her displays of affection, he does return it on occasion.
He does not kill without reason, though it doesn't seem to detract from his enjoyment of his job's brutal nature, as he is commonly seen grinning during challenging fights. Between himself and his partner, Shin acts as the more observant of the two, and usually remains calm and collected to counteract Noi's impulsiveness.
He always eats fast and sleeps with one eye open; this is an old habit from his past life in Hole, which he developed after almost being lynched by people who found out he had Magic User blood in his veins.
Shin's magic allows him to slice up anything. He can use this ability to slice up living beings without worrying about the victim bleeding out and dying from organ failure, although their flesh will still rot. Any current victim of his magic would immediately suffer the consequences of their wounds if he were to die. Shin is also capable of projecting his Smoke to stop incoming gunfire. His Smoke halts and shatters bullets on impact. Since he was born unable to actually utilize his magic at will, Shin had to cut his hands and arms in a self-inflicted surgical procedure to find the smoke veins.
Shin was a resident of the Hole. His mother was a Magic User killed by the Hole's anti-magic user militia not long after his birth, while his father, who he shared a modest home with, was human. Shin managed to hide his origins and blend in with Hole's other inhabitants by working at the joinery. His father was employed as a carpenter until he accidentally cut himself during work. His boss, after seeing that his blood was mixed with Smoke, an indication of someone being a magic user, quickly notified the militia. Trying to protect his son, Shin's father was immediately killed for marrying a Magic User, although he was fully human. After defeating his father's three murderers, Shin went into hiding for about three months, committing various small crimes and murdering the militia members coming after him.
He was found by Kasukabe and Vaux in the operation room in Hole's hospital. There Shin, who was unable to produce Smoke, had cut off his fingers and arms using Vaux's medical equipment to find the vessels which produced the magic substance, which would allow him to realize his full potential. Aided by Kasukabe, he was finally granted the ability to produce Smoke (at the expense of both his arms, which he asked to have stitched back to his stumps). Later he escaped to the magic users' realm after having mutilated the rest of the militia with his new-found powers.
During his time in the Magic User realm, he stole food from one of En's restaurants, and met Noi, the restaurant bouncer at the time. She pursued him, confronting the thief demanding to pay for what he stole. Noi healed his arms to kill him in a fair fight, but Shin stabbed the back of her head with his claw hammer and flew away, promising to make up for what she did for him. Thus, leaving a bleeding and angry Noi on the floor to heal.
Time passed, and Shin was hired by En to become one of his bouncers (due to his mutilation type of magic). He and Noi became close friends, beating people for En and talking about how dumb he was for his business ideas (like a stupid jingle composed and interpreted by himself for his restaurant) until the day of blue night came. Two shady Magic Users Baku and Yaku, who wanted to beat them and then kidnap them both to sign contracts with them so they would use them as "Forced Partners" (the contracts signed in the blue moon night sometimes obliged one of the partners to do what the other says unquestionably). They fought and seemingly killed their aggressors, but not before the beheaded corpse of Baku shot one last time at Noi. Shin took the hit, and his back was flayed in the process, finally making up for what she did for him before, giving him a chance to live thanks to his healed arms. Shin told Noi not to heal him so she could become a Devil with no regrets, but she relinquished her devil hood to save him, since that day, he and Noi became partners.
Shin appears for the first time in chapter 4 of the manga, during a cleaning mission with Noi. With his claw hammer, he kills some of the remaining Cross-Eyes members in a hideout to take an elderly unnamed Cross-Eyes to En. Nothing more than a head, the target was put in a cheap body bag and accidentally splashed all over Noi, to her disgust and Shin's annoyance. Subsequently, they met En at a restaurant, dressing for the event (Shin just average smoking, feeling ok to wear what was normal to him). There, En entrusted them the mission to find and kill Kaiman and Nikaido (Due their Magic User hunts in Hole, they killed Matsumura and injured Fujita, now present in the dinner with Ebisu, another of Kaiman victims).
Leaving to the Hole at the Day of the Living Death, they found them and engaged in a fight, Shin was really excited to fight, engaging Kaiman in a one-on-one fight using his claw hammer, seriously hurting him. Kaiman swallowed his head, and Shin noticed the man inside Kaiman's head. Shin used his remaining strength to chop his opponent's head in a single swing of his claw hammer. Nikaido saw this, and while Noi overpowered her, she took the body and head of Kaiman, opened a Magic Door, and escaped. The cleaners came back to the sorcerers' realm believing that Kaiman survived somehow and needed to find him. Shin was among the rest in Turkey's house to make a doll of "The man inside the lizard head", following the doll through the city until they found a box inside an old building. There the doll went berserk and almost killed Fujita and Ebisu. Shin destroyed the doll while Noi nursed the two. They opened the box to reveal a rotten head. Noi fixed it with her magic, showing that the head belonged to "The man inside the lizard head mouth".
- Because of his childhood in the Hole at the whim of magic users, Shin has a habit of eating quickly. He can eat faster than Noi.
- During one of En's balls, he unknowingly danced with Noi, who was later to become his partner.
- According to En, Shin is Noi's most treasured person.
- Shin usually wears his mask backward, ironically, making him look a bit less frightening. He wears it correctly when he gets serious, however. Oddly enough, despite the fact that En doesn't like him wearing the mask backwards, Beelzebub himself puts it on him that way.
- Noi refers to him as "Senpai" even though she's been with En for longer than Shin. It's probably because he has been a Cleaner for a long time while she was assigned much later.
- His name is an alternate pronunciation for the 心 (heart) kanji. This is a recurring theme on his character, as his mask is shaped like a human heart, and his magic door has "EL CORAZON" (Spanish; lit. The Heart) written on it.
- He is Gura-Gura's (former) owner.
- He seems to be very one-note when it comes to fashion; most of the time, he's wearing a suit with sneakers or sports clothing when he's working out. Previous to the Blue Ball, he explicitly states he has no more criteria for his outfit outside of it being black.
- He first started using a traditional curved-claw hammer as a weapon when killing the militia group that murdered his father, since he already had it at hand as part of his work attire. There is a chance that is the same hammer he uses today.
- Shin's name 心 uses the kanji for heart