Quirks are a significant part of My Hero Academia's hierarchy, one that ostracizes those without the gene and puts the #1 Pro Hero on an unattainable pedestal. While many are physical and quite self-explanatory, such as Mashirao Ojiro's Tail Quirk or Mount Lady's Gigantification, others require more explanation.
One of these would be Aizawa Shota's Erasure. Known by the hero name Eraserhead, Aizawa is a teacher at U.A. High School, helping train children to master their Quirks and become integrated heroes in society. Erasure allows the user to cancel out the Quirk of anyone they look at, making them a far easier opponent to battle. There is an interesting science behind Erasure, mainly focusing on the type of light the eyes glow with when in use.
How Does Aizawa Shota Work in the Dark?
Aizawa is known by students, other heroes, and fans of My Hero Academia as being permanently tired. The bags under his eyes and his scraggly appearance are telling of his lack of sleep, but there's an honorable reason behind his perpetual exhaustion. Aizawa spends most days teaching his students in Class 1-A, then patrols the streets at night as a Pro Hero.
Eraserhead's eyes glow red when he uses his Quirk, a color of light that doesn't glare as others might. This would make night vision not only possible but easy for Aizawa, as his pupils wouldn't have to keep re-adjusting to the dark and light sources when he's on patrol. This would also decrease eyestrain and keep his field of vision clear at night, all while providing a light source. Red light is also difficult to see at a distance, so when his Quirk is in use, Eraserhead's position still wouldn't be compromised.
How Does Aizawa's Erasure Quirk Work Scientifically in My Hero Academia?
As previously stated, Erasure deactivates another person's Quirk, but when Aizawa is using this his physical appearance gives away some science behind the technique. His eyes glow red, his hair floats, and somehow the enemy's power is snubbed out. It so happens that red light has a longer wavelength than other colors, which allows it to penetrate the body easily. Red light and infrared light are even used in medical imaging to detect things under the skin.
In short, the red light emitted when Aizawa uses his Quirk allows him to reach an opponent's Quirk gene to temporarily disable it. However, it's not the light itself that immobilizes the gene; this is most likely done through the use of an electromagnetic field. The light spectrum is a small part of the electromagnetic spectrum, so it makes sense for both to work hand-in-hand in Eraserhead's Quirk.
The most familiar electromagnetic force people experience day-to-day is static electricity. When MHA's Aizawa switches on his Quirk and his hair begins to float, this is likely due to static electricity coursing through his body as Erasure begins to work. Essentially, it's like when a cat gets rubbed with a balloon and its fur sticks up and is drawn to the source of static.
Erasure works by emitting an electromagnetic field that penetrates the skin just as the infrared light from his eyes does. Electricity can be fired at DNA to switch genes on and off in real life, so if this same technique is applied, Erasure could target the Quirk gene and temporarily immobilize it with electricity.
Erasure is an incredibly powerful Quirk in My Hero Academia, but is often overlooked because it doesn't look as flashy or strong as One For All or Hellfire. However, in the hands of All For One, Aizawa's Quirk could easily amount to the end of the world -- or at least the end of any AFO opposers. Eraserhead only uses his Quirk to disable another's Quirk gene, but in the wrong hands, Erasure could seriously maim or even kill an opponent with just a look.