Aery Doesn't Work with Everything?

How come aery will proc wth Brand's passive but not Darius'? It seems a little unclear on what aery can and can't activate with whatever ability and any champion. Certain spells I understand, but the situation like this with 2 very similar passives, makes it very unclear on what runes you can use for certain champions and their abilities. If there was rundown for what your rune page does for your champion, it would help people a lot with what runes and keystones they want to have with their champion. Going in blindly and assuming it works because it does for other champions and finding out it doesn't, makes it very hard to continue playing the current match and scary to experiment with other combinations in future matches.