I found something... interesting (or really unpleasant?) on the wiki:

Negate Damage
This ability completely negates an enemy's attack. Even if the attack would do multiple hits, all hits would be nullified.

This ability does not stack. You can only have one damage negation barrier on someone.

If the flower knight evaded damage in some other fashion such as evading the attack or the enemy missing, the damage negation barrier would not be consumed. This means that an evading flower knight that can negate damage will have that barrier ready to activate for her the exact moment her dodge fails.
source: https://flowerknight.fandom.com/wiki...ty_Particulars

This ability does not stack. You can only have one damage negation barrier on someone.
That's really anoying. But I'm glad I read this before I use my R-medals for Tritonia (I like her but I wanted her to use her with Maid Cowslip and get double barrier).

So... I wonder who I should get now?