L'Arachel -def or -hp?

If you're not using a special that scales on Res like Glacies or Iceberg, or a ploy, -res will be better than -def in the long run.
Especially if you use horse emblem buffs on her at that point she may even be able to take some hits on her def from greens.
Your aim is getting her into Desperation anyway so after the first fight you're not supposed to take any more hits, and with that having 3 less points in res won't change that much while 3 less points in def may kill you.
In general the best bane is res if you're not making use of it and you have more res than def and you can survive more phisical hit by not taking - def

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