Shigaraki's quirk is known simply as 'decay'. As the name implies, it is a quirk that allows its user to decay or destroy anything that they lay their hands on.
Kyudai Garaki, Shigaraki Tomura was able to receive the power of All For One from All For One, who kept a duplicate of the power for himself. This Quirk was passed on to him after a long surgery and made him every bit as fearsome as All For One himself.
After being reprimanded by his abusive father for discovering a picture of their estranged grandmother (Nana Shimura) in his father's study, Shigaraki suddenly manifests his quirk Decay at the unnatural age of five, which causes him to accidentally turn his entire family to dust.
All For One (オール・フォー・ワン, Ōru Fō Wan?) is the Quirk used by All For One, before being transferred to his successor, Tomura Shigaraki, while keeping a duplicate.
Shigaraki Tomura was born with a real curse: a dangerous, unstable Quirk called Decay, that makes anything that he touches crumble to dust.
Fans know that his name is Hisashi Midoriya and that his quirk is fire breathing. It's assumed that Hishashi's fire-breathing quirk isn't as eye-catching as Dabi's flames since Inko brushed it off at Izuku's doctor's appointment as a child. Currently, Hisashi's work has taken him abroad, leaving Inko and Izuku alone.
Former Abilities. One For All: All Might inherited the Quirk called "One For All." It would allow him to stockpile an enormous amount of raw power, allowing him to significantly enhance all of his physical abilities to a superhuman level.
Yoichi Shigaraki is the younger brother of All For One. In the past, All For One deeply loved and cared about his younger brother, as he was the only family he had. All for One and his younger brother.
Life Force, All For One, One For All, Fa Jin, Gearshift, and the unnamed Luminescence Quirk are the oldest known Quirks in the series.
The first person to manifest a Quirk was a newborn baby in the city of Quig Quig, China, who had the ability to emanate light from their body. After that incident, many people around the world began to manifest different kinds of special abilities, though the cause of the phenomenon was unknown.
Izuku was raised primarily by his mother Inko, who has the ability to make small objects float towards herself. His father, Hisashi, whose quirk allows him to breathe fire, is not seen due to him working abroad in the United States.
Bakugo's Quirk is rather simple, however, the way he uses it makes it a genius ability. In normal circumstances, Bakugo has access to just one Quirk, however, in My Hero Academia's second movie, titled My Hero Academia: Heroes Rising, Bakugo ends up receiving the One For All from Deku.
After being mortally injured by All Might years ago, All For One's face was entirely made up of scar tissue, extending from above his upper lip and covering his entire head and the back of his neck. As such, he had no visible nose, ears, hair or eyes, though the outlines of his eye sockets were visible.
As you can decipher, Tomura's quirk of decay is seemingly having an adverse effect on his body, with the constant scratching not just being a sign of his emotions, but his power as well. With his ability to make anything decay with a touch, the side effect appears to be an annoying one.
1 Eraserhead Would Nullify All For One's Power
Thanks to Erasure, he can nullify the quirks of other individuals, thus turning All For One into a normal human. The one downside is that Eraserhead needs to see this target's full physical body, and his eyes must stay open in order for Erasure to remain active.
He explains that All Might's shabby presentation possesses black eyes as a result of becoming a shadow of his former self. The loss of his mentor, his deteriorating medical state and years of shouldering the public's need for stability in a tumultuous world all wore him to near-fatal exhaustion.
1 Shigaraki
All For One is arguably the rarest and most powerful Quirk possessed by any villain in My Hero Academia. This Quirk so thoroughly defines its bearer that he's taken it as his name. All For One's Quirk lets him steal Quirks from other people and use them as though they were his own.
His Quirk is Explosion (爆破), which allows him to make explosions from his hands by detonating the nitroglycerin-like substance he sweats; throughout the series, he learns various different ways to apply this.
How It Works. Deku's final quirk is known as 'gearshift'. It's a quirk that is activated via physical contact. It allows the user to change the velocity of anything they touch, meaning they can spontaneously slow things down, or speed things up.