I don't want... you to die. Because... my big brother... is... the nicest person... in... this world.
— Genya Shinazugawa to Sanemi Shinazugawa in Feelings for Elder Brother, Feelings for Younger Brother
Genya Shinazugawa (
At the time of his debut during the Final Selection, Genya was a short, young man with large, inward-slanting eyes. The space where his eyebrows would've been is constantly furrowed, which gave him a permanently angered appearance. His hair is styled into a buzz cut, with only a small clump of messy black hair left to grow on the top of his head. He also possessed a large, jagged scar that ran over his right cheekbone from his ear and to over his nose.
During his first appearance, Genya is seen wearing a purple, sleeveless yukata over a plain black shirt with long sleeves.
Later on, when seen again in the Butterfly Mansion, Genya had a much more feral appearance, having undergone a growth spurt that put him at almost six feet tall. His hair is also much longer, worn in more of a mohawk style, the strands much longer and visible around his neck. It is also noted that he became more muscular and gained many more scars all over his body.
After the Swordsmith Village Arc, his hair gains bright yellow tips.
After becoming a Demon Slayer, his outfit changed to a dark olive-green version of the Demon Slayer uniform, over which he still sported his old purple yukata.
Genya is initially a foul-mouthed and ill-tempered individual; a "lone wolf" who refused any help from others and did not show any interest in being polite or having any manners. During the Final Selection, he roughly handled Kanata Ubuyashiki by grabbing her hair and yelling at her. His ill temper and brash way of speaking heavily resembles that of his older brother, Sanemi.
He became more open to cooperation during the battle against Hantengu, an Upper Rank Demon, where he worked alongside Tanjiro Kamado, Mitsuri Kanroji, and Nezuko Kamado. After some time, he learned to become more sociable and less ill-mannered towards others, particularly towards Tanjiro and his friends.
Sanemi's refusal to acknowledge Genya also made him insecure as he came to realize just how weak he is compared to his companions. Nonetheless, he did whatever he could to help his allies, even if it got him horribly maimed in the process. Despite his brother's harsh rebukes, he bore no ill will towards him, a belief reinforced by Tanjiro and eventually by Sanemi himself.
Demonic Transformation: By consuming the live flesh of a Demon, Genya could temporarily gain demonic attributes from it. Depending on the strength of the individual, he could gain regeneration and physical strength equal to one. In this form, Genya is capable of overpowering Aizetsu briefly.
- Upper Rank Four Empowerment: After consuming the wood created by Zohakuten, Genya had enough strength and speed to throw 3 trees in quick succession. In his battle against Kokushibo, the full extent of his demonification upon eating some of the Upper Rank 4's flesh is shown that despite Kokushibo viciously bifurcating him across his abdomen and cutting of both of his arms, he still did not die, showing that like a genuine demon, Genya could now only be killed by decapitation.
- Upper Rank One Empowerment: Upon eating the hair of Kokushibo, Genya's demonic abilities were further enhanced, as seen when he managed to reattach his severed body in mere seconds and is even able to intercept the telepathic communication of Muzan Kibutsuji. Upon eating a piece of the Upper Rank's Flesh Sword, Genya even began taking up several of Upper Rank One's physical characteristics such as his eyes and hair. Later, the full extent of his enhanced demon abilities is shown that even when he is bifurcated and half his head is sliced cleanly in half, Genya is not only still alive and conscious but still possessed the necessary strength to activate his Blood Demon Arts. However, upon succumbing to his severe wounds, Genya much like a genuine demon, disintegrated to ash.
- Flesh Gun: Genya displayed the ability to detach his cells and merge them with his gun, with the gun having the same characteristics of Kokushibo's sword of having multiple eyes on top of the barrel and muzzle, which presumably increases its accuracy and power.
Repetitive Action: A technique taught to him by Gyomei Himejima to help him compensate for his lack of talent and aptitude to use Breathing Styles. This Technique mainly focuses on Genya repeating a set of words or phrases that assists him to focus on his given task properly and keep his mind clear and block out pain. For Genya, he repeats a set of prayer of the Amida Sutra to help him focus and steel his mind, as seen where he used this technique to focus his mind after being fatally injured fighting Hantengu's Clone Aizetsu and to a degree, replicate the effects of Total Concentration Breathing.
Due to having eaten the flesh and cells of at least two Upper Ranks (Kokushibo and Hantengu), Genya had seemingly developed his own Blood Demon Art while in the heat of battle against Upper Rank One. Similarly to Nezuko's Blood Demon Art, Genya's own were also tailored to battle and do damage to other demons.
Wooden Flesh Bullets: Due to eating the cells of Upper Rank One and Upper Rank Four, Genya had developed a unique technique where he merges his demon-transformed cells with his sun steel bullets and gun, that, when fired, the direction and velocity of the bullets could be freely manipulated by Genya to easily move around obstructions between the bullet and the intended target, as seen when his bullets moved around Kokushibo's sword, directly burying themselves into his flesh. Once inside its target, the bullets can immediately grow into a gigantic tree similar to the tree creatures of Upper Rank Four's Zohakuten form and then entangle and wrap around the intended target, paralyzing them.
- Blood Roots: Genya could further alter his embedded Flesh Bullets by having them take root inside his target and suck the demons blood from inside their bodies, effectively preventing them from activating their own Blood Demon Arts.
Expert Swordsman: Before he opted to use a shotgun, Genya's main weapon was a short Nichirin Katana, and it was implied that he was decently proficient in using it against demons.
Nichirin Shotgun: Genya harbors a western double-barreled shotgun he uses for close and ranged combat proficiently. The bullets he uses are made of Scarlet Crimson Iron Sand and Scarlet Crimson Ore, allowing him to kill demons without a blade.
Nichirin Short Katana: Genya also carries a shorter Nichirin Katana two hollow ovals that overlap its core and are a dull shade of brown for its handguard.
- Genya's surname contains the kanji for "immortality" (不死 shinazu?) and "river" (川 gawa?). His first name contains the kanji for "mysterious" (玄 gen?) and "all the more, increasingly" (弥 ya?).
- Genya is one of the few characters in the series who does not primarily use a sword and is the only Demon Slayer named who cannot use any of the Breathing Styles.
- Instead, he uses a technique referred to as Repetitive Action, which acts as a substitute for Total Concentration Breathing. It's important to note that this technique was taught to Genya by Gyomei, who himself is a Breathing user, implying that it is possible to use both techniques in conjunction with one another.
- Generally, Genya is better at wielding a gun than a sword, as he's very good at hitting targets.
- Kokushibo mentions that Genya is not the first Demon Slayer he has encountered that consumed Demons to gain power.
- It seems that Genya is shy around women, breaking out into a blush and losing the capability to speak with them. This is seen when interacting with the Love Hashira, Mitsuri, and the younger girls who work at the Butterfly Mansion.
- Due to his unique Demon-eating powers, Genya regularly goes to the Butterfly Mansion for health check-ups.
- Genya ranked 15th place in the second popularity poll with 2589 votes.
- Genya shares the same Japanese and English voice actors as Garfiel Tinsel from the anime Re:Zero − Starting Life in Another World and shares the same japanese Voice Actor of Liebe from Black Clover, Nishinoya from Haikyu!!, Bakugo from My Hero Academia and Ghiaccio from JoJo's Bizarre Adventure.
- (To himself) "Can I do this? Can I be any use? Will he notice me right away again... and cut me in half so that's the end? Sanemi... I can't let him die... I definitely mustn't fail. Himejima... Tokito... If only I were stronger!! If I were a Hashira!! The more I want to help, the more my body stiffens up making it difficult for me to move. I'm scared... that I'm no use and can't protect my comrades. Why am I so weak? It's frustrating! It's frustrating to be weak."
- (To himself) "I'll do it. I'm gonna do it. I have to do it. Think only about winning. I will not let my brother, or my master, or any of my comrades die!" 
- (To Sanemi Shinazugawa) "I don't want... you to die. Because... my big brother... is... the nicest person... in... this world."