Remember that guy from earlier? I told you he'd be important! You see instead of sharing the sun's gift, this guy, Tomura Shigaraki, hoarded it's healing power and used it to keep himself young for hundreds of years. And all he had to do, was sing a special song.
Flower gleam and glow,
let your power shine
Make the clock reverse,
bring back what once was mine
What once was mine
All right, you get the jist. He sings he turns young, creepy, right?
But even he couldn't stop the flower from being found.