In A Sky Of A Million Stars (Who Cares If One More Light Goes Out?)

Summary

He could never forgive himself. It was his fault. He’d planted the idea like a seed he’d never known would grow.  (Or: What if Izuku jumped?)(OR: The one where Izuku jumps and lives and Katsuki visits him every day and Class 1-A not-so-secretly finds it adorable that their designated angry pomerania

Author's summary from Archive of Our Own.