Ten Lifetimes Of Ash by AEORAJI

Nine lives. Nine deaths. One name carved into every one of them. Shen Qinghe was once Heaven's most gifted healer. Then the Demon Sovereign Xie Wuyan cursed him into the mortal cycle, and for nine hundred years he was born, broken and buried. In his tenth life, he wakes up remembering all of it. So he does the only sane thing: he walks into the Demon Realm with a scalpel and a grudge. But Xie Wuyan doesn't fight. He doesn't even look surprised. He offers a bargain instead. Stay one hundred days in his crumbling palace, and if Qinghe still wants him dead at the end, he will kneel for the blade himself. Qinghe agrees. He has waited nine lifetimes. He can wait a hundred days. He didn't plan on the Sovereign's terrible jokes. Or the way he flinches when Qinghe coughs. Or the locked hall with nine shrines, and an empty chair beside them. Some debts are paid in blood. Some are paid in lifetimes. And some can never be repaid at all.