Izuku Midoriya was thrown into the river by his mother so he couldn't suffer the same fate as his parents. He spends the next 12 years growing up with boars and strengthening his body. Deku becomes the self proclaimed mountain king and when strangers enter his territory he will find a way back into society and enter UA. And with the help with old friend Bakugou and new friend Ochaco, he will remember his past life.

Izuku moved from Bakugou's tormenting to a random neighborhood not to far from Yuuei. There he finds two notebooks, called 'Thunder Breathing' and 'The fight against Muzan'. Next to it was a sheathed sword. What will happen when Izuku learns how to use Thunder Breathing and gets into Yuuei? What will happen once a new demon appears and he is the only one that can kill it?