it is revealed near the end of the story that a major character was dead the entire time and was replaced by someone else. however you never actual meet them before they die
the game has two monsters based on demons
the Sutsune who is a combo of a Kitsune and a succubus
and the Stolby based the demon prince Stolas who looks like an owl
one major area is an ocean were you need to go underwater. however the game does not feature any large sea creatures and there is no breath mechanic so you can be underwater indefently
The game features 2 spider monsters. One is a silver spider with wings and the other is a collective swarm of spiders intelligent enough to disguise themselves as a human.