The identity of the "something else"?

What do you think the souls of the otherworldly beings - that Chariot Requiem was eventually transforming everyone it'd affected into - were? They were never specified and remained a complete unknown; a loose end that never really seemed to go anywhere beyond establishing an arbitrary time limit to steal away the arrow (and one that, I might add, felt somewhat forced to create artificial tension in the story, considering it was tense enough due to Diavolo having insidiously possessed one of the heroes and trying to get the arrow before them anyway).

While it may not have been particularly relevant to the overarching story (essentially being an unnecessary caveat to Requiem's ability, since it didn't have to have an "objective" and, IMO, didn't really improve the pacing of this arc at all), I still think it's one of the strangest elements of Part 5 that was barely touched upon and actually kind of glossed over.