Kuromaro

Kuromaro is a fallen god said to bring eternal darkness wherever they were called to, living in isolation from other gods and beings. They have two forms, appearing to Nanami as a male and to Ookuninushi as a female.

On her second trip into the past, Nanami manages to get another deity to call Kuromaro, yet it's only during the third trip that she gets to meet them and hear about their connection to Tomoe.