Shiki Nanaya is an alternate version of Shiki Tohno created from his subconscious and given form in a number of different ways throughout the Tsukihime storyline.

Nanaya is always calm and composed, and he is prone to making sarcastic and witty comments. He is fixated on death and killing, and the mere prospect of it brings him the utmost joy. He calls his body a guiding principle that Shiki refuses to use in his objections to becoming a killer. He is originally just something that kills whoever summons him, but he later develops an attachment to existing. He mentions having been sleeping when he did not exist, and that there were people to play with on the "other side", though he could not kill them because they were all dead people. Although obsessed with killing, he displays somewhat normal interactions with people like Miyako Arima and Hisui.