Seven Days - Yann Beauverd

The narrator woke up one morning in someone else's body, exactly a week before his friend took his own life. The whole thing felt unreal and disturbing, but all he could think was, This is my chance to change what happened. At first, it seemed simple enough: figure out why, find a way to stop it. But it didn't take long before he realized there was a lot more going on. He kept bumping into hidden lives and buried secrets-stuff nobody ever talked about. Day by day, the pressure built up. Each new discovery made things messier, not clearer. He found himself scrambling, desperate to piece everything together before the tragic end.