From now until we're up to date with DMM, it goes in this order (of Union Events):
Pride (Light)
Sloth (Water) [Christmas Event]
Envy (Dark) [Mid January]
Lust (Wind) [Early February]
Greed (Phantom) [Late Feb/Early March]
Gluttony (Thunder) [Mid March]
Wrath (Fire) [Mid/Late April]
Sloth 2nd [Mid/Late May]
Lust 3rd [Mid June]
Pride 3rd [Mid July]
Envy 3rd [Early/Mid August]
Greed 2nd [Early/Mid September]