Been thinking about Present Mic's Quirk a lot lately and I actually found some evidence to suggest that his Quirk is a lot different from how we normally think about it.
His Quirk is listed as an Emitter type and a lot of people seem to portray it as him simply being able to amplify his voice or make sounds with his mouth that create shockwaves to attack his enemies. Very similar to someone like Black Canary of DC Comics fame. But the thing is, I don't think that his Quirk really has to do specifically with shockwaves, and I don't think that his Quirk works with just any old type of sound that he could potentially make with his mouth.
His Quirk is called "Voice." Rather than thinking of his Quirk as an amplification Quirk that makes his natural voice louder, I think his voice is his actual Quirk, and I think he can adjust the output of his voice in both directions: both low volume and high volume. It's just that speaking at a volume quiet enough that a normal person can't hear it isn't useful for attacking villains, so we only see him using his Quirk to be loud.
But the name of his Quirk isn't the only evidence I have for this theory. There's also the fact that he was born with his Quirk. As a general rule, Quirks tend to manifest at the age of 5 in most children and the only time you really see exceptions to this rule are with mutant or mutation type Quirks. For instance, Ojiro and Iida both have mutant type Quirks. They were given extra body parts by their Quirks and they've had these extra body parts since birth, even if they didn't know how to properly utilize them (Ojiro's tail and Iida's engines, for example).
Mutation Quirks aren't exactly the same, but they're similar. Mutation Quirks are often extremely powerful Quirks caused by gene mutation. They seem to manifest out of nowhere and are usually Quirks that aren't passed down to them from their parents like other Quirks are. Mutation Quirks sometimes manifest earlier than 5, such as Eri manifesting her Quirk between the ages of 2 and 3. This is also the case for the glowing baby, who had the first Quirk ever due to some kind of gene mutation and had glowing skin from birth.
Hizashi has had his Quirk since birth, and it's stated in the introduction of his Quirk that he made the ears of his parents and the hospital doctors bleed with his first cry. If his parents had similar Quirks to him, wouldn't they have anticipated something like that and been able to wear noise-cancelling headphones or something similar?
Just to use Black Canary for comparison again, she can mimic sounds and she primarily creates shockwaves by screaming or whistling. Most people portray this as being the same for Hizashi, but we just don't have any evidence to support the idea that he can mimic sounds or that he can whistle to create shockwaves. We've seen him whistle in canon before but never while using his Quirk at the same time. In fact, the majority of the time that he's using his Quirk, he's talking while doing it. Talking at extremely high volumes rather than simply yelling or screaming
One of the only times this pattern is broken is during the war arc, where he does actually just scream to break all the Nomu tanks. But even at that, him yelling and screaming still utilizes his vocal cords whereas something like whistling does not.
The last bit of evidence that I have for this theory is the fact that in Vigilantes, it's shown that Aizawa can use Erasure to silence Hizashi's voice. No, he's not just canceling out any volume amplification, he's LITERALLY erasing Hizashi's whole voice.
Hizashi was speaking at a normal volume in this panel, but his voice gives out entirely while Aizawa in the next panel over has his hair floating, the tell-tale sign of his Quirk--as well as a smug grin on his face.
This would suggest that, like mutation Quirks (such as Ojiro's tail and Iida's engines), Aizawa can erase the function of Hizashi's Quirk even though the body part is still there. Meaning that Aizawa erased the function of his vocal cords, though the vocal cords stay intact. If Hizashi's Quirk was simply that he could make his voice louder, then Aizawa would only be able to cancel out the volume but not necessarily Hizashi's voice as a whole.
So, I think "Quirk: Voice" should be taken literally! I think that Hizashi's voice IS his Quirk and that he has crazy control over his vocal capacity with both the ability to make his voice loud enough to shatter eardrums and quiet enough that the normal human ear couldn't hear it. The latter ability could certainly have its own uses. This also might lend to the possibility that if he can change the volume of his voice, he might be able to change pitch, tone, and other aspects of his voice with ease. He might be able to mimic other people's voices or change the sound of his voice at will! Wouldn't that be an interesting piece of information, especially in regards to a young student who just got moved to the hero course...?
