in the JP wiki it is translated wrong a lot, that why i had to triple check the names when I made my list.. but notice when it's originally in japanese, all the normal event say "イベント報酬" like apocalypse, phoenix, rahab etc... literally meaning "Event Reward" when translated into english.. it says the same thing in japanese for the Vritra battle, but it's weird cause when you translate page to english it say "event fee" instead. but that just wrong translation, so don't worry about it.. it's just a normal event