Since Kill Joe's soul is this doll, he can't longer possed a person without feel weak when he is out of his doll.
But with Haru, his present self is a little different, Joe can't possed his mind, but he can change Haru's body he can make Haru looks exactly like him, change his clothes or toake them off, can make Haru a older version of him, can make haru have a fuzzy body, and make him a woman.

Kill Joe do this things because he wants to Haru feels the despair of the humillation, but this isn't work at all because Haru already made a lot of shit in his childhood and adoslence!!

PS: When Joe "posses" Haru body, Haru's eyes continue the same as his normal default dragon form!!