Most of my research is a miss-mash of Internet sources, books and my own rough supposition. Although the great thing about fiction is how much you can make up by your own imagination, I do try to gather as much facts as I can, especially when dealing with myths.
As mentioned before, Inugami are a type of tsukimono (憑き物 or 憑依物), meaning they are capable of possession. The word tsuki is the key, meaning the act of possession.
There was a time in Japan when people showed signs of being possessed, it was thought to be the result of an animal spirit possession. There were ways of ridding the person of a possession, but as you can imagine, they were pretty brutal. Some of the more popular suspects for tsuki were the fox (kitsune), the Inugami or the cat (nekomata).
For the youkai who were capable of possession, there were also people who controlled them – the mochi (使). Further, there were families that had these youkai as pets, for lack of a better term – suji (筋).
Suji and mochi seem to be used somewhat interchangeably. But families, as mentioned before, ‘inherit’ the tsukimono down the bloodline, catering to them in return for wealth. There’s usually a moral in these myths and in this case, it’s a ‘careful what you wished for’ scenario.
Mochi is also the name of a Japanese sticky rice cake. So, chew on that 🙂