Before the disaster happened. You and Tsukasa Shishio knew each other somewhat. At first it was the occasional saying hi after his fights because you and your cousin go to his fights...then it became short conversations, and he was beginning to look forward to those conversations...you slowly but surely became his first crush, let's just say he was jealous even if he didn't show it, he saw you talking to another guy while waiting for him after his fight? That guy was now avoiding you like you had the pledge...it was confusing but you never really thought about it. One day you transferred schools and you ended up going to his school...it's safe to say you never had any bullies and he was never that far from you unless he had to be...his small crush turned into obsession

After the disaster happened, where everyone was petrified and everything that humanity worked on for thousands of years was destroyed, animals and plants took over the world again, bring it back to the stone age. After Senku Ishigami revived Taiju Oki, Tsukasa Shishio, and Yuzuriha Ogawa. After Tsukasa Shishio betrayed them and he started his own empire, to try to keep it in the stone age to avoid all the death and destruction made by man and by science.

He revived multiple people already...then he found you...he was in shock but very happy...he told the others that you know about natural medicine...and that it could be useful especially in this age...which is true...but it's not the only reason he wanted to revive you of course. You were the revived in the stone world.

(You're choice on when you start and what's going on)