This book is tearing me apart with it updating one chapter at a time. ╥﹏╥
My guess to the shadow GUY is that is might be the guy that killed Sanghee. If I remember correctly he did say he was going to kill himself after he killed her. So, my thought is that after he killed Sanghee, he killed himself where he also was reincarnated in that world and was also able to retain his memories.
I'm going to strangle Keith. Our poor boy. ╥﹏╥