But deku could have been born with DECAY and All For One could have taken his quirk because Inko asked him to and gave it to Shigaraki around the same time because 21-16=5 so when deku was born he could have manifested his quirk and All For One gave it to ShigarakiSo Shigarakis quirk was originally Deku'sAnd All For One is most likely Deku's fatherIt's actually a Star Wars reference Because All For One represents Darth Vader so Deku may represent Luke Skywalker Darth Vader is the main villain so is All For One. Deku is the main hero representing Luke Skywalker
How would he have decay? They said his mom's quirk is attracting things to her, and the dad's quirk was breathing fire. And they also said the things with the toe joints.