I have the White key for the top of the gate but it says "It looks like you don't have the key to that particular lock"
https://imgur.com/a/roMINrO
I haven't had the time to fully explore it myself, but my understanding from my brief read-through of the event is that the monsters will drop determination fragments (there are three different types), and you have to collect some combination of them all in order to increase your determination. Other methods are killing elite monsters, as well as clearing the Black Mage's chains, which appear in a map after the 11th elite monster has been spawned in a map. I'll come back and edit this response if I find out any conflicting/different information.
as you know the first level 200 was a warrior and the first level 250 was a lumi, so please someone pick a different class for the 275 first place spot, any class