Early on in the series, Genya had a short build which stood slightly above Tanjirou Kamado. He had short, messy back hair that what shaved off at the sides. thin eyebrows, and a scar that covers most of his face's width.
Later on, he reappeared with a wilder look as his height changed significantly, making him taller than most and now has longer hair reached down to his neck. He also gained a large, muscular build along with this as well as various scars all over his body.
Genya is a foul-mouthed and ill-tempered individual with a "lone wolf" character who refuses any help from others and does not show any interest in being polite or having any manners, much like his older brother.
Sanemi is Genya's older brother and only living sibling. After a demon attack befell their family, Sanemi and Genya were the only ones who survived the incident but after Genya branded his sibling a "Murderer", their relationship began to worsen and decline until the two splits and went their own ways. It was revealed during the battle with Kokushibou that despite the whole incident, Sanemi still cares for his younger brother and actually wants him to live a normal life. Genya was moved to tears and apologizing after hearing Sanemi reasoning behind his rudeness.
At first, Genya treated Tanjirou like an annoying pest and wouldn't even talk to him. This didn't discourage Tanjirou who kept wanting to connect to Genya, which just pissed him off. However, throughout the fight with the demons, Genya starts connecting to Tanjirou and gains respect for him. Tanjirou also tried to mend Genya relationship with Sanemi, although his actions earn him a mouthful from the higher-ups.
Genya belonged to a family of nine with a hardworking mother who never slept and deadbeat father who would occasionally beat her despite her weak build-- including the children as well.
Some time later, Sanemi had learned that their father had gotten stabbed to death and made a vow with Genya to protect their siblings and mother.
One day, their mother had gone missing and didn't return almost until daybreak. As suspicion and worry began to cross the minds of the children, alone and unprotected, a loud knocking sound was heard from their door which they presumed to be their mother but was a demon instead which immediately killed off 5 of the 7 children and scarred Genya.
Leaving no moment for Genya to escape, the demon soon came for Genya but was interrupted by Sanemi and later went into battle with him and told him to "run for it!!"
Shortly after, Genya went to call a doctor for his injured siblings but soon stumbled across Sanemi who had held the demon at bay and successfully killed it with the help of the sun but was unprepared as the demon who attacked his family was none other than his mother. Greatly confused by what happened, Genya panicked and chose to place the blame on Sanemi and call him a murderer for killing their mother and tricked himself to believe it was a wolf that attacked the family instead.
Later in his life, Genya realized his mistake and tried to reconcile the relationship with his brother. He trained to become a Demon Slayer, however he had an inability to use Breath Styles. However he discovered that he could eat demons and gain demonic abilities. He was discovered by the Rock Pillar Gyomei Himejima. Since Genya couldn’t use Breaths, Gyomei didn’t make him his Tsuguko, but he still decided to train him. At some point he met back with Sanemi and tried to apologize, but Sandmi rejected him calling him wearing and saying he had no brother. On this, Genya decided to become a Pillar to gain some connection with his brother.
Genya participated in the Final Selection exam, managing to survive the seven day trial. He impatiently inquired about receiving his Nichirin Blade, angrily hitting both his Kasugaigarasu and one of the proctors when his demand went unfulfilled. He was then grabbed by Kamado Tanjirou, who promised to break his arm if he didn't immediately let go of his second victim, something Genya dared him to do. Tanjirou obliged, leaving the irate youth to nurse his broken limb, with the choice for the alloy of his future sword then presented to him.
Later, at the Butterfly Estate under unknown circumstances, Genya intentionally tried to bump into Tanjirou, ignoring his greeting afterwards. He later received the report of Kyoujurou Rengoku's death via Kasugaigarasu, in the company of Himejima Gyoumei.
Genya later appeared at the Swordsmith Village, ignoring Kanroji Mitsuri's asking of his name, and is found by Tanjirou in the hot springs. The scarred youth ripped one of his teeth out and discarded it, accidentally hitting Tanjirou with it. He turned when his name was called, angrily told his fellow Demon Hunter to drop dead, and plunged his head into the hot water when he persisted in talking with him. He also didn't show up for any meals, having told the villagers he wouldn't eat at all. When Tanjirou went to bring him some leftovers, he wasn't in his room.
A few days later, Genya listened with impatient anger as Tanjirou explained the situation with Hotaru Haganezuka and the rusted Nichirin Blade, and then exclaimed that he didn't care and that Tanjirou shouldn't talk to him as if he were his friend. He reminded his companion that he had broken his arm, told him not to call him by his first name, broke the rice cracker Tanjirou offered him, and told him to get out. He fell silent when Tanjirou pointed out his regrown tooth, telling him that he must be seeing things, but was disgusted when his companion showed him the tooth in question. Telling him to throw it out, the scarred youth kicked Tanjirou out of his room.
Genya appeared during Tanjirou and Nezuko's battle against Hantengu, aiming his gun at the former Upper Moon's staff-wielding form, Sekido. He shot a cluster of bullets at the Demon, completely decapitating Sekido but failing to completely do so with Karaku. Moving in to finish the job with his Nichirin Blade, Genya ignored Tanjirou's advice, proceeding to complete Karaku's decapitation. This lead to the two Demons becoming four, and Genya was stabbed through the chest by the spear-wielding Hantengu, Aizetsu. Aizetsu attempted to pull the spear out of Genya to attack Kamado Nezuko, only to be unable to do so. The scarred youth then shot at the surprised Demon, blowing his head to bits. He noted that the headless Demon was starting to pull his spear free, getting a horrendous slash wound across his chest as a result. Genya began to pray, avoided another attack from his opponent, and attacked the spear-wielding Demon from behind. He was foiled in this attempt by electricity from Sekido, firing a counterattack at the offender. Aizetsu attacked him once more, this time managing to smash him into a wall. Undeterred, Genya began to pray again, answering his opponent's question of what he was by introducing himself, promising to kill the spear wielder.
Later, Genya managed to defeat his opponent, spearing him to a tree and ripping his head off. He turned to face Tanjirou, his appearance changed to closely resemble a Demon's, grabbing him and telling him not to push his luck, as he would kill the Upper Moon. He goes on to deny Tanjirou's defeat of Upper Moon Six and states that he will become a Pillar before him. When Tanjirou happily agrees to this, even offering his support, Genya tries to call his bluff, only to see in his comrade's eyes that he was telling the truth. They were then interrupted by an electricity attack from Sekido, with Tanjirou heading off to find the Upper Moon's fifth body, telling Genya not to attack Nezuko. Genya headed northeast at Tanjirou's direction to find the fifth Hantengu, noting with frustration that he still couldn't see him, only to finally notice him, a small version of Hantengu's original form. The scarred youth shot at his tiny foe, then attempted to cut his head off with his blade, only for it to break. He shot at the tiny Hantengu again, only for this to also not work. He was then ambushed from behind by Sekido, apologizing to his older brother for "what happened back then", noting that he only wanted to become a Pillar so his sibling would accept him. However he was saved at the last second by Tanjirou and Nezuko, but after Hanetngu’s hatred forcefully combines with his fellow aspects into Zohakuten, he attacks Tanjirou. Genya was just about to shoot the demon, but Zohakuten used his Blood Demon Arts to turn the trees into dragons. When Tanjirou proclaims his hatred for the demon and his mentality, Genya was shocked that the kind boy had any anger in him.
When Mitsuri Kanroji arrives and starts fighting Zohakuten, he goes to protect her when the demon stuns and nearly kills her. Mitsuri gets up and continues to fight the demon and Genya, Tanjirou, and Nezuko get constricted by the wood dragons when they go to get Hantengu's main body. Genya decides to eat the dragon around him, not only to free Tanjirou and Nezuko, but also get absorb demonic abilities. When they destroy the wood dragon and get to Hatengu's protective orb they find that the wooden sphere is empty. When they spy the small demon, Tanjirou yells that he won’t get away. However Genya, fed up with the demon’s crap, throws a freaking tree at the demon. Somehow he misses, so he, Nezuko, and Tanjirou give chase. Tanjirou, emulating Zenitsu’s Breath of Thunder, rushes at the demon with blinding speed. However, Hantegu's resentment causes him to split again, creating a larger body around himself, while he is hidden inside its heart. When Hantengu grabs Tanjirou, Genya goes to his aid. He pries the demon's hands off and then rips off his arms, while Nezuko shoots fire at him. However the flames start hurting him, since he at the demon’s blood art and is partially a demon. He has to curl back so the fire won’t spread to him, leading Hantengu, Nezuko, and Tanjirou to fall off a cliff. Genya, to injured to move, yells at them to see if they are alive. Tanjirou decapitates the resentment demon, but after its body starts attacking some villagers and the demons tongue that has the kanji for resentment on it, he realizes that it was a fake and Hantengu is escaping. Genya starts climbing down the mountain to help Nezuko and Tanjirou, but he was to slow and Nezuko had to kick Tanjirou towards Hantengu at the cost of her apparent death. When Tanjirou finally slays the demon, and it's discovered Nezuko can stand in the sun, everyone celebrates. Even Genya cracks a smile.
Abilities and Powers
Demonic Transformation: By eating a demon, Genya can temporarily gain demonic attributes from it. Depending on the strength of the individual, he can gain regeneration and physical strength equal to one. In this form, Genya was capable of overpowering Aizetsu briefly. Later after consuming the wood created by Zouhakuten Genya had enough strength and speed to throw 3 trees in quick succession,and in his battle against Kokushibo where he was brutally cut into pieces,his demonification was further enhanced as he managed to survive despite his torso being severed into two and his two arms were amputated and upon eating some of the Upper Moons hair,his transformation was accelerated further to the point that he could now hear Muzan Kibutsuji's telepathic orders being sent to Kokushibo.
- Genya is one of the few characters in the series who does not primarily use a sword and is the only character so far who cannot use any of the Breaths.
- It seems that Genya is also shy around women, breaking out into a blush and be unable to speak with them. This is seen when interacting with the Love Pillar, Kanroji Mitsuri and the younger girls who work at the Butterfly Estate.