@hulog To answer your questions
Spoiler!
Popo was an ordinary fox who was saved by Shiho who loved every being, be it animals, human beings or divine beasts equally. This monster who had the sword was a human being who was saved by Shiho as well and she died but a part of her soul was transferred in Popo and that's why he was able to talk. After this Popo disappeared forever with Shiho. The connection between Shiho and Ari is just that Shiho's marble is in Ari I think 🤔 and thr ML is Ari's teacher, the black tiger/panther. In the last chapter of Story Ari kissed him on cheek while Baekryeong was ready to kill him. I don't know if there are any more chapters or side stories after that 😅
I like to post spoilers for the stories I find interesting because I don't have much time to read novel due to busy schedule
you will find me in most romantic historical manhwa comment sections 
you will find me in most romantic historical manhwa comment sections 