Shikigami

Shikigami (式神) are a kind of spirit summoned to serve that person. They could be thought of as "familiars".

In InuYasha, Shikigami came in the form of Tsubaki's Hebi (snake/serpent), and Kocho and Asuka, the two girls who accompany Kikyo. There were also others, but those two come to mind as the most obvious examples.