Thanks EpicFail for the advices.
I don't have Rabbit's Foot (who is a package of everything needed here) and it's too late to get her now I think. I considered using Cardamine for Pierce and Skill rate x2 next turn.
I'll try various things.
And I just realized there is a x1.1 sun damage 4* memory. Good to replace my missing x1.1 sun dmg 5*.