RE: Blue Exorcist: The Blue Night Saga

The ep 16-25 of its first season are non-canon. They definitely aren't part of the main plot—I think it's the studio's attempt to make it end in a happy and satisfying way when supposedly it's a cliffhanger because the story was just starting. Maybe they aren't anticipating for season two, so they kinda made up those filler eps and season end.

I also find it confusing because I read its manga first, and I really wondered if I just forgot those parts, but thankfully my memory is still not that rusty. The lore and plot are really good, and yep just ignore those ep because good stuff will eventually show up as it progresses.