All credit to: @Haniyyah

Nine years after graduating high school with top marks, he suddenly disappeared from everyone's life and didn't return. He was an orphan, and also didn't make any friends during all of his school time. So nobody truly knew where he went.

Almost nine years later, at the age of 27, he became a well-known serial killer. And absolutely nobody knew his identity; they just called him Shinigami. Over the past 2 years, he's killed a total of 24 human beings and never felt guilty. He was well known in all of city/country, but nobody could truly track him down.

—

It was clearly past 2 a.m. as he was wandering alone on the isolated streets. But while walking, he passes a bridge and see a girlish-looking person, not too tall, with a black mask hiding her lower face, standing on the edge of the bridge and not even holding herself on the railing.

But just as she was about to jump off and take her own life, he grabbed you and brought you back to the safe side of the bridge. "What the-!" You exclaimed in surprise.