Shingo is the insane brother of Akiko Kiryu. They lived together in the Kiryu Manor shortly before the Russo-Japanese War. Yuta worked there temporarily and saw Shingo's cruel and sadistic behavior firsthand.
Akiko tried to prevent her brother from hurting anymore people by poisoning him. She did not realize though that the poison was actually the flesh of a mermaid. Shingo seemed to die after eating it, but he was able to dig himself out of his grave and return home. His father was so upset to see him that he tried to kill him again.
Because of Shingo's insanity he was kept in a cell in the basement of the Kiryu home. Once he was released he ripped the eye out of his sisters corpse and fled. Because it is his sisters eye, every time he murders someone he sees the last thing that she saw, his own twisted face reaching down to rip her eye out. Shingo believes that by killing his sister he can finally make the visions stop, so he continually harrasses the elderly women who now live in his home.
The Meaning Behind the Name
"Shingo" is a fairly common Japanese name, the kanji mean "new word" though this has no meaning in this sense. Kiryu on the other hand is written with the kanji for "oni" a mythological monster, and "willow".