Twenty years prior to the beginning of series, he mysteriously vanished. Upon his return to the town, he was chased up a tree by a dog and was rescued by Nanami Momozono. As thanks, Mikage bestowed his home and mark to Nanami through a kiss to the forehead. He is seen helping Nanami when she loses faith in herself or when she is confused or scared about what to do as the Land God.
He returns to help Nanami save Tomoe from a curse, though he originally said he's going to say goodbye before Tomoe dies. He was the one responsible for making Tomoe forget about his past love, saving him until he fell in love again, this time with Nanami. He was also the one responsible for turning Tomoe into the type of character he is in the present, most likely saving him from the death of his curse.
Mikage was visited twenty years prior to the main series by Nanami, who explained both the events of the series and that she knew how to save Tomoe. As she informed him that, in the future, he has been absent for twenty years he knew he must leave the shrine. He is also kind of a crybaby, as in the flashback, Mikage cried because he thought that he scolded Tomoe too harshly.