A short story taking place in a world where people known as Killer Demons have each mastered a specific form of killing. Satsujinki to Deep End and Satsujinki to Never End follow a different character's encounter with one of those Killer Demons.

Satsujinki to Deep End was originally submitted for, but did not win a Dengeki contest before Toaru Majutsu no Index was published. It was later published in 2004 in response to Index's popularity.