Myrrh usable???? ;(

The Myrrh I've been using for months now on my Dragon team is +Speed -Defense (arguably the worst IV) and she still does work, even if her defense is lower than it should be, with Fury and for exemple the Atk/Def +2 seal she still works wonders. She's often defensively buffed by my Ninian too.
The only problem with a -Def nature imo is that if you want to give her DC in A slot instead of Fury, you might lack a bit in Defense, but that's nothing you can't solve with buffs !

+Atk is a good boon for her, and 32 Def is still good enough to deny doubles from a good amount of people. If you want to run her on a general team, try and get one of her teammates to use the Def Tactic seal. With Fury and Def Tactic 3 she'll be at 41 Def which will deny doubles from everything that's not an armor unit, who likely won't have the speed to naturally double her anyway