Fukushuu Kansuisha no Jinsei Nishuume Isekaitan

Kousuke Kurono was a young man consumed by darkness. After a devastating tragedy shattered his world, he dedicated himself entirely to a singular purpose. For years, he walked a path of vengeance, becoming someone unrecognizable from the innocent boy he once was. When his long-sought goal was finally within reach, Kousuke found himself at a crossroads where his life's purpose had been fulfilled, leaving him adrift in an existence that had lost all meaning. Just as he was about to make a final, irreversible choice, a mysterious voice intervened with a question that would change everything. When he next opened his eyes, Kousuke found himself in a realm beyond imagination - a completely different world where his story would begin anew. (Source: Joeglens blog)