Iridatsu Yuuta spends most of the series as a ghost. The ghost is shaped just like Yuuta, but with ghostly lower body-ish.
But later we learn that
Yuuta's body is not his own. Yuuta's is actually Pine from the lab children flashback, has white-ish hair. The body he is inhabiting actually belongs to Narugino/Chiyoko.
What is the in-universe reason that Yuuta's ghost is shaped like that, given the information above?
I can guess at the out-of-universe explanation, it is pretty obvious that
Were his ghost to be diffferent from the body, it would spoil the disclosure of the body switch plot.