I am Mizuki. Snake familiar now serving Momozono Nanami along with Tomoe-kun.
Age: 400+ (looks around 18)
Unlike the main familiar of the series, Mizuki was not a demon, but hatched from an egg for Yonomori, the water deity that the humans created. When she was not needed anymore and the humans stopped visiting the shrine, she died, living Mizuki behind to take care of the temple.
Many years later, he meets Nanami at her school, while he was looking for a bride and marks her as his fiancee. Nanami doesn't realise it and finally, he kidnaps her only to find out she doesn’t want to be his bride. Tomoe rescues her and she promises to talk to him seeing how lonely he was. Later on, he becomes her familiar, without her consent in order to save her from a demon that wanted to steal her God Mark.
These days, I spend my time watching over Nanami, taking care of the Mikage Shrine, our home, and arguing with Tomoe-kun.
These stuff are known for people who read the manga/watched the anime.
1) Mizuki doesn't get drank by his own sake, but you can easily get him drunk with everything else.
2) Mizuki doesn't need to eat to survive. This my assumption since he doesn't know how to cook. We also know that Yonomori didn't need to feed, but only drank sake, which only leads to the fact that Mizuki wouldn't eat either.
3) His favorite food is candies/pastries/anything sweet.
4) Although he fights with Tomoe, they have some moments where they cooperate and talk as friends, especially since the incident at the vacation. (won't reveal more, read manga!)
5) He knows about Tomoe's past.
6) He likes to see Nanami as a goddess and a goddess alone, and dislikes when he sees her human, clumsy side.