I created this theory and it is my little headcanon. The reasons for this are simple:
Attributes of quirks are shared between families
Both Uraraka and Shigaraki need all five fingers to touch something for their quirk to work
We learn about Shigaraki's dad's side of the family but never his mom's or her quirk, so the mom would very well have a brother, sister, or cousin that is Uraraka's parent.
This is a small theory. Tell me what you think. I would love to hear your ideas on how it could or could not be real.
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Todoroki's mind (aka bnha theories)
FanfictionThese are theories I heard or thought up. I will say If and why I do or don't believe them and leave it open for discussion. Not all might be relevant, but I would like to hear your opinions on them. WILL CONTAIN MANGA SPOILERS YOU HAVE BEEN WARNED