I am American mentally, with Japanese tendencies.
'Worldbreaker <name>', 'Harbinger <name>' or possibly '<name>, Cataclysm's Ruin'... something with a little zest. 'Avenger of the Five Flights' just sounds bland.
<Name> the Dragon King
Avenger of the Five Flights sounds rather lame, but when you think about it more, it's actually pretty awesome.
Rairu - Mage
(Name), Death's Demise
Oh wait I already have that one!
Maybe start a list of name they probably wont use. Pretty sure they will not use the following words in the title.
King, defender, twilight, black wing or bane, dragon slayer, vanquisher, Defender of.
I'd have to go with World breaker as well