Can you tell that I've been reading a lot of vigilante AUs?
Art by awkwardcolbysstuff on Tumblr
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Vigilante Tommy AU where his power is that he can understand and speak any language in the universe.
When he first starts up as a vigilante, people assume he doesn't have a power because he never uses one when he fights. That is, until he calls The Blade a pussy bitch in perfect Ancient Greek. At first, everyone just assumes that he just somehow knows how to speak a dead language, but then, just a few weeks later, he uses his power again. This time, he starts reciting the Declaration of Independence in Medieval French to confuse Siren so badly that he manages to avoid being mind-controlled.
The thing is, Tommy's ability also allows him to understand and repeat hybrid vocalizations, for example, avian bird noises, raccoon hybrid chittering, cat hybrid hissing and meowing, piglin noises, etc. He also has a habit of unconsciously starting to make hybrid noises when he's around hybrids, a habit he got from being roommates with Tubbo and Ranboo. This comes to light when he eventually encounters Philza Minecraft himself and accidentally starts chirping.
This sets Phil's dad senses for two reasons:
1 - Tommy (or whatever his vigilante name is) was making fledgling chirps, meaning that Phil now has a general idea of how old Tommy is and that he's way too young to be fighting crime by himself.
2 - Fledgling noises make bird brain go brrrr and now Philza wants to adopt a new child.
So Phil (for some reason not telling the other heroes/hero commission how old Tommy really is) tells Wilbur and Techno that Tommy is but a child and that's how the found family shit starts, because Will and Techno were already a little fond of the feral vigilante, so knowing how young he is just adds them to the "People Who Want To Adopt Tommy" list.
Extra Idea: Purpled is also a vigilante that Tommy encounters on patrol one day. Purpled is also secretly an alien, and as soon as they start talking, Tommy is compelled to speak in a certain way. He just lets it happen because that sometimes happens when he talks with Ranboo, it means that he's compelled to speak to the person in their native language (it happens most often with people whose first language is not English and also hybrids with species specific languages, like Endermen and Piglins. Similar to unintentionally making hybrid noises, but different.) So he opens his mouth and starts speaking to Purpled in his planet's native tongue, and Purpled is fucking FLOORED.