When he found out he had no talent as a swordsman, he felt mentally exhausted. His mental state pushed him into a corner. where he ended up eating a demon. Then he discovered this idiosyncrasy as his own ability.
Genya has abnormally strong jaws and with this, he's able to consume the flesh of demons. When he does this, he takes on their appearance and sometimes parts of their abilities as well.
Demon Consumption & Empowerment: Genya possesses unnaturally strong jaws and special digestive organs which allow him to tear off and consume the flesh of demons without any adverse effects. By devouring demon flesh, Genya gains demonic characteristics, such as fangs, dark sclera, and unique yellow tips in his hair.
Genya also gains the characteristics of the demons he consumes. His physical strength increases, and he also regenerates, just like demons. His jaws are unnaturally strong, which helps him tear off demon flesh. His unique digestive system allows him to stomach the flesh.
For a short amount of time, he can become a demon using his bite strength and his special digestive organs." Basically, as a result of his serious gnashers and iron stomach, Genya can devour demon flesh and gain characteristics like the sharpened fangs, frosted tips, and black pupils seen in the most recent episodes.
Unknowing that his mother was the demon, or "wolf", Genya screamed at Sanemi and labelled him as mother's murderer, an action that he reminisces regretfully.
Genya's weapon in Demon Slayer
However, that takes away his ability to use breathing techniques, which is why Genya is unable to master swordsmanship.
Genya is always angry at others because of everything he has gone through in his early life. Every waking moment is an attempt to become stronger, even if it is at the expense of his life. He is doing this only for his brother to acknowledge him.
Siege and Storm
Alina urges Genya to come with them but Genya cannot and is left behind. Towards the end of the book when the Darkling finds Alina, we find out that the Darkling unleashed nichevo'ya on Genya because she spared Alina. Her skin is scarred all over and she only has one eye left.
Alexander III wants Genya to be beheaded for high treason and murder, while it becomes clear that he raped her. Genya confesses that she poisoned her own skin so that the king would consume it when he kissed and touched her.
The most accurate assumption to make here would be that he cannot perform concentration breathing and improve his breath. This is something that is quite intuitive and the main reason for his inability to perform said techniques is probably because he lacks the natural talent to do so.
Genya is the first of all Grisha to share her specific talent, and she is curious, knowledgeable, and kind. But she is also tool used by the Darkling to endear himself to the royal family by gifting her talents to the queen (and making her body easily accessible to the king, who sexually assaults her).
He fired a bullet that not only damaged Kokushibo, but also sprouted roots that trapped him to the ground. This allowed Gyomei and Sanemi to deliver the final blow on Kokushibo, killing him soon after. Unfortunately. Genya succumbed to his injuries and his body crumbled away as Sanemi held him.
No one killed Sanemi Shinazugawa. Sanemi almost died when he tackled his sister Genya from a window in order to protect her from a demon attack, but was saved by his friend Masachika who healed his wounds.
More importantly, Genya is able to become stronger after consuming a demon. For the most part, Genya gets an enhanced physical constitution (which makes up for his inability to use Breathing Styles) along with potent regeneration.
Demon Slayer: Kimetsu No Yaiba, Volume 20 continues as the Demon Slayer Corps' initial confrontation with the most powerful of Muzan's demons, Kokushibo, has left Tokito severely wounded and Genya cut in half.
Genya Shinazugawa is the student of Tokyo High School and Sakura Igarashi's crush. He is also the Sanemi Shinazugawa's younger brother. He later snatches Demons Driver from Hikaru so, Genya can temporarily become Kamen Rider Over Demons to stop the chaos by Fenix & Demon Slayer Corps.
Genya is moved to tears and apologized after hearing Sanemi's reasoning behind his rudeness. After their battle with Kokushibou, Genya apologized again for blaming Sanemi and thanked his brother for protecting him before succumbing to his wounds and crumbling into dust, leaving Sanemi stricken with grief.
He asked impatiently about getting his Nichirin Sword, striking both his crow and Katana violently when his request went unfulfilled. Tanjiro interfered, if he didn't let his hands off Kanata immediately promised to break his arm. Then, when Genya dared him, Tanjiro pushes, leaving him with a broken limb.
The emerald green blade also represents wind breathing and is seen by Wind Hashira, Sanemi Shinazugawa. The abilities that come with his green sword is being fast like a tornado whilst also staying extremely calm.
Genya is considered a weaker Demon Slayer, since the Upper Moon 1 acknowledged him to be the smallest threat during his battle against Genya and multiple Hashira. However, Genya can absorb a demon's power by eating part of them, gaining its abilities, and shaping them into his own unique Blood Demon Art.
Genya was killed by the Upper Moon 1, Kokushibo, but not before helping the others take him down. As he was dying, his brother Sanemi regretted how strained their relationship have become, and wept as he begged the heavens to spare Genya. Like a demon, his body disintegrated as he died.
Despite this crude and reckless battle style he managed to survive and kill several demons, later upon looking back at his past exploits Sanemi admitted that the only reason why he survived was due to sheer luck and the unique aroma of his blood that caused the demons to become intoxicated, drunk and less focused in ...
Genya's tragic past
Genya's flashback explains how they had an abusive father, who used to hit his children and wife frequently. After their father died, the two brothers stay close, and the responsibility of looking after their family falls on Genya and Sanemi.