That was EASILY one of the best chapters. I want to see this animated in a future anime season so baaad. Q-Q Please, we all need to invent a time machine to make the anime much more popular than it was, just to make sure we get it!
So miko's father has a regret so he can't leave yet. So like the dog of the family, maybe the previous hipo became the beast after long time without passing away, so it could happen to the ghost lion. So there is a reason some humans don't become a bad ghost (I bet the black suit ghost were human) and animals become eventually. Miko's dad hadn't become a shadow yet but the dog.
It might be the offerings. Giving offerings in the correct way offer “safe” food for them, limiting the corrupting influences. The father was well fed all his unlife, and he had a strong sense of self and duty, that also helped him. The dog had the duty, but as an animal, a weaker sense of self, and he probably kept eating random non-offering, and he slowly got corrupted. (I wonder if him having such an human name guided his “human-like mutations”, like it confused him, making him believe he was, actually, a human? XD )
The men in black are getting offerings so the don’t progress, but they were probably found too late… or just constantly fighting monstrous ghosts eroded them?