I’ve got a couple of my Valkyries to level 65. With all the buffs and XP Boosts during the event, it’s not that hard. The trick is to run a couple of dungeons though. I ran the Armory twice on one character and the Armory and the Catacombs each on the second character. With both of them I reached 65 before going inside the fortress for the final battle with Dakuryon. Things were a lot easier at the higher level, even though you don’t get a better weapon and I didn’t bother going back for the better armor.