... episode 4 but it probaly has something to do with an alternate timeline, which is my guess atleast. He didnt meet the photographer guy until the end of the festival when they entered the ritual building and he got to meet Shion
I dont think the ovas are that important, they seem very filler-ish. Also correct me if im wrong here but doesnt the main storyline have 3 seasons? (Koro Ni, Kai and Rei)
Additionally, there are several other OVAs, but most of them are random non-canon stuff. Only one of them is actually canon, as far as I know, but it's an unimportant side story.