I managed to clear both Ragnaroks, though Phoenix only barely. As Aidoru suggests, it's probably best to let the buffs expire. I didn't have time for that though so I brought 2 dispellers.

With my primary team Apocalypse never got off a Rage overdrive. That makes the fight significantly easier. Phoenix is a pure DPS race. She's going to KO your kamihime 1-by-1 with triple attacks, so you need the DPS to finish her off before your party is dead. Blind, dizzy, and multi-hit rate down will help buy you some time.

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So the event shops are... not what I expected. The reward tiers haven't reset; instead, one copy appears to be set to the old tier you were at, while the new copy is at the highest tier. I have a sneaking suspicion the shop is bugged in our version.