So I just thought of a cute AU for the My Hero Academia universe in particular.

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So basically when you turn 16 you get a tattoo on your wrist. The tattoo is made up of two small colored-in circles -outlined in black- next to each other, the first one is your hair color the second is your eye color. When you get it, it shows you what your new hair and eye color will be. The new colors you get, are the exact opposite of your soulmates. So their hair color is your new eye color and their eye color is your new hair color, and vice a versa. And that is how you now look to everyone else but you, in the mirror       you look the way you always did. Whatever haircolor and eye color you had when you were born is what you see in the mirror. Now here's where it gets complicated. There are rules. If someone dyes their hair, they are the only one who can see it. When you see your soulmate you don't know at first. Why you ask? Because other than them, you're the only one who knows what they really look like. Other than pictures and someone pointing it out to you, you won't know how you look to other people. Even though most people have phones, it can still get confusing. Only when you and your soulmate fall in love with each other your hair and eye color turn back to normal. So if you fall in love before your soulmate does, you'll have to wait until they fall in love with you too. For some people who believe in love at first sight it's easy, but for everybody else it's kind of difficult.
But let's say if your soulmate dies, then automatically your hair and eyes will either turn a different color or it'll go back to normal. So you'll either get a new soulmate, or you don't, and that means you're meant to be alone.

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Let's give some examples shall we?

* So everyone knows Todoroki has half red half white hair, and blue and grayish-brown eyes. His soulmate would have half grayish-brown, half blue hair, and half red, half white eyes, talk about crazy.

* Iida has blue hair and (for the sake of cannon) originally wore blue contacts not so he can      see but because of his family, because unlike them he has red eyes. So his soulmate has blue eyes and red hair.

* And when I said it could get confusing, this is the one I meant. Kirishima naturally has black hair and red eyes. But to his soulmate he has red hair and red eyes because they hadn't seen him before he dyed his hair. So his soulmate has black eyes and red hair. So unless he told them, his soulmate wouldn't know.

* This is also one of the confusing ones. Aizawa. If your soulmates quirk has something to do with their eyes, the color that they turn when they use their quirk, -if you're quirkless- that is the color of your hair. So because Aizawa's eyes glow red when he uses his quirk, if his soulmate has a quirk, when they use it, their hair glows red. Otherwise they have black hair and black eyes.

* The easy ones are as followed:

- Bakugou's soulmate has yellow eyes and red hair
- Midoriya's and Tsu's soulmates have green hair and green eyes, obviously
- Uraraka's soulmate has Brown hair and brown eyes, obviously
- Monoma's soulmate would have light blue hair and yellow eyes.

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But now that I think about it, because there are characters who have eyes and hair that match, it's going to be a lot more difficult for them to find their soulmate. Especially when you have characters like Midoriya and Tsu in the same class. Also Uraraka.