Her Hundredth Sacrifice, His Eternal Regret

To revive her dead fiancé Ethan, Nora signs a system deal to finish 100 redemption quests in a magic realm. She sacrifices her heart for the final task, only to find she’s tricked. Magical world’s Kane, betrayed by his white moonlight and bereft of Nora, gets the same system and arrives in Nora’s modern world, meeting her and amnesiac Ethan.