Sojobo's Room, Mount Kurama, Kyoto
"Trouble still brews in Yomi no Kuni."
"I want you to come to Shinjirou and teach him the barrier techniques, Suiro."
"S-sojobo-sama?! I thought no one is allowed to leave the mountain until the Nura Clan reseal the fox?"
"My direct son may be safely hidden in the human world, but he barely mastered learning the basics of hiding his youki before he left the mountain."
"I do not want to take any chances of my estranged brother learning of his whereabouts and as our kind knows, Shinjirou is still missing."
"That brother of mine is a fool for following that hungry fox."
"As the leader of the clan, I want Mount Kurama to be close to protect its people, but as a father, I yearned for my son to be here in my sight."
Your presence may help in protecting the human god's home. I believe she is away to find Okuninushi's soul ."
"I entrust you to give this letter to Shinjirou."
Did some research, Tataranuma and Mount Kurama are real.
As for the Mikage Shrine, there are at least five shrines in Google Maps so I choose the one realistically nearest Tataranuma-Ome City, Western Tokyo.
TV Tokyo Building was seen in the anime, so I used it as a possible clue of KH's location.
Expect a longer one because I always publish a 1k-2k word chapter/story. This is only the warm-up.