The Quirk In My Hero Academia That Makes No Sense To Fans
The world of My Hero Academia isn't too far removed from our own, but for one quintessential difference: Close to 80% of the population is born with superpowers called Quirks. These inborn abilities come in all shapes and sizes, from the literal size-changing Quirk of Mt. Lady (voiced by Kaori Nazuka) to the explosive capabilities of Katsuki Bakugo (Nobuhiko Okamoto). Quirk usefulness certainly varies, but those who put in the work toward becoming heroes can produce surprising results no matter how they start out.
Luckily, series creator Kōhei Horikoshi makes most Quirks easy to understand, either through extensive demonstration or story progression. Characters like All Might (Kenta Miyake) and his protégé Izuku Midoriya (Daiki Yamashita) do a bit of both, and knowing the full scope of their shared Quirk — One For All — makes watching them fight extra satisfying.
What happens, then, when someone's Quirk doesn't fully make sense? Viewers start asking questions, putting the show's very fundamentals to the test. It might be okay if it's a background character or an extremely minor side character, but as MHA fans discussed on Reddit, there's one fairly important character whose Quirk doesn't quite add up: Mirio Togota (Tarusuke Shingaki) a.k.a. Lemillion.
What is Mirio's Quirk?
Compared to all the hard-working characters who attend U.A. High School, a training ground for those aspiring to become professional heroes, Mirio initially appears to be an extremely laid-back guy. Between his friendly demeanor and strange sense of humor, it's hard to believe he's considered one of U.A.'s so-called "Big 3" — that is, one of its top students — along with Tamaki Amajiki-Suneater (voiced by Yuto Uemura) and Nejire Hado-Nejire Chan (voiced by Kiyono Yasuno).
Using his Quirk, called "Permeation," Mirio can make any part of his body — or his whole body — intangible at any time, allowing him to pass through walls, solid objects, and even enemy attacks. Significantly, when returning to a solid state, he is propelled out from whatever he phased through at tremendous speeds. In learning to combine these two aspects of Permeation through years of focused practice and tireless dedication, Mirio can move about the battlefield almost as if he's teleporting.
U.A.'s Class 1-A is arguably the most impressive group of up-and-comers the school has to offer, but in the aforementioned scene, Mirio takes them all out in no time at all. By constantly slipping in and out of his peers' vision. He appears for a moment, lands a solid blow, and disappears a moment later — rinse and repeat. "Mirio's Quirk isn't one to be jealous of," Tamaki thinks to himself as the beat-down continues. "What you should be jealous of is his skill." Indeed, Mirio was considered the man who would replace All Might until Izuku stepped in.
The problem fans have with Mirio's Quirk
As amazing as it is to watch Mirio in action, fans still have their qualms with the mechanics of Permeation. Intangibility is intangibility, after all, meaning he doesn't experience air, light, or sound while using his Quirk. So, as u/Unforeseen_blind points out, if he's not affected by light, shouldn't Mirio become invisible whenever he activates Permeation? Furthermore, as u/Th3Grimmi says, shouldn't Mirio's last meal tumble to the ground as well?
Toru Hagakure (voiced by Kaori Nazuka), a member of Class 1-A, actually does possess an invisibility Quirk, though it works a bit differently than intangibility does. As noted above, intangibility should affect the way light interacts with Mirio; Toru's Invisibility is based on light refraction, however, which is not at all the same thing. This is seen when she uses her Super Move, Warp Refraction, to manipulate the light around her to shine brightly at others. With Permeation, Mirio doesn't "touch" light in the first place, meaning he can't replicate any of Toru's abilities.
As for the food question ... that's a little harder to answer, especially after watching Mirio's clothes fall off during his practice bout with Class 1-A. There's really no explanation for this one, and most of the fans in the Reddit discussion agree that the way Horikoshi designs Quirks is more like magic than science. There isn't an overarching magic system that defines the limitations of all Quirks, of course, but it's a valid point.
If Horikoshi ever decides to implement hard science into MHA, then questions like the ones asked of Mirio would increase tenfold. As it is, viewers can either choose to suspend their disbelief or not. Indeed, suspension of disbelief comes into play for any superpower. Theoretically, for example, a giantess like Mt. Lady shouldn't be able to support her enormous body, but she does. If it means enjoying the character, then the exact scientific details don't always need to matter — and Mirio is definitely a character to enjoy.