there's a lot of broken toys behind him (the ripped teddy bear, the rusty-looking van), and we all know that Tsukasa is extremely sadistic to the point of sexual abuse, so it's either some kind of remnant that was left behind when Tsukasa and Amane died, or after the severance they were bound to the place they lived in when they were alive. I'm leaning more towards the "remnant" theory because Hanako and Tsukasa were ghosts bound to the school when people died there.