I'm a librarian who loves anime, manga, and reading a wide variety of genres.
I don't know if it's immortals in general that are creepy, or just Chihaya. He seems to at least dislike being in pain, but his attitude towards war is weird (war is nice because now he has a really excellent horse). He has the ability to switch bodies with animals at will, and it never seems to occur to him, or he doesn't care, that the animals aren't necessarily going to be okay if they get injured while he's using them. He, meanwhile, can recover from what would normally be fatal injuries in a day.