Couldn't all for one have given Shigaraki decay quirk? I mean why would Horikoshi add this if this scene wasn't important?
looking at this picture, we see that shigaraki's decay was used by another person (quirk), which means that Shigaraki's quirk was actually someone else's quirk, which was later given to shigaraki.
Chapter 350. We see Afo wearing a fedora. We see someone who looks like AFO come to the Shimura house. Maybe he gave Tenko the decay quirk to humiliate Nana.














