Yonomori Mitsuha ( 夜の森) is the Water God who silently looks over her village. Her shrine was built by the people of a village because a big river near their village often washed away children and they feared it was a curse. However, as a god born to met the needs of the people in her village, she disappeared when the people of her village left.
She loves the plum blossom tree outside her shrine that was paused on the peak of it's beauty. The tree was the last thing that reminded Mizuki of her.
Her avatar is plum blossoms.
Mizuki was her snake familiar that she had hatched from an egg. He is very special to her and vice versa. Nothing is truly known about the relationship they had. But in a flashback that Mizuki had, Yonomori was shown asking him about if he had a girl he liked, which he replied of course not, to which Yonomori replied that if he ever found a good girl to watch the flowers with, than he had to tell her right away. Before her death coming, Yonomori made a plum blossom tree, making Mizuki promise her that even when she was gone, that he would still smile and be happy. In other words move on with his life and become a happy person. Nanami stated that she didn't want him to be lonely. She loved him enough that she wanted him to be set free of the familiar title.
When Nanami travels back into the past, she comes across a young Mitsuha, sometime before she had a proper shrine and before Mizuki was hatched as her familiar. In the duration of Nanami's stay in the small Yonomori shrine, the two of them develop a fondness of each other.
When Nanami is about to leave in order to resume her journey in the past, Mitsuha waves to her and tells her to come back to Yonomori Shrine, wherein Nanami finds out that the little goddess is in fact Mizuki's beloved Yonomori-sama.
In the end of the chapter, Nanami states quietly that she could already see her shrine and her honest familiar surrounded by peach blossoms. She even stated that meeting Yonomori was a beautiful and good thing.
He is the god who had given Yonomori the egg which contained Yonomori's familiar, Mizuki. Not much in known about their relashionship, but it is hinted that he is her father mainly due to her having a flashback to when he had stated that she was a weak goddess while giving her the egg.