This is great! I've always loved serial killer stories and this story has the same irresistible features. The tension of the first part, the mystery, "Today was the first time I've ever seen you," the sheer obsessiveness of the both of them. And I really like their interaction in this one: Touya's jealousy, Shindou's hesitance and possessiveness, their competitiveness.

It seems that a serial killer AU should feel more surprising than it does, but then -- "In Shindou Hikaru's entire life, only three things have held his attention for more than a few weeks – Go, murder, and Touya himself" -- it does share some qualities with canon. I really like all the canon references here, how essential Go is to their thinking and even communication, and the different meanings Sai and Touya's frustration when he was twelve have in this universe.