Like I said in the Tiering thread, I tought about a team for Kerria...

Kerria
+40% ATK for her and 2 allies
+40% DEf for her and 2 allies
Insane damage buff depending on her HP
80% Evasion first two turns, 50% after.

Dancing Lady Orchid (Bride of Fos)
+18% ATK for all
x1.2 skill act for all
+10% skill damages for the team (and +20% for herself)
-15% ATK for all pests

Lavender (Valentine)
+15% ATK for all
x1.2 skill act for all
+15% damages for all on bosses
-15% ATK for all pests

Aconite (promoted)
+20% ATK for all
x1.36 skill act for all (based of the girl's skill level but Kerria will be max skill)
-20% ATK for all pests
+random panel stuff

White Tulip (promoted)
+22% ATK for all
x1.2 skill act for all
-20% ATK for all pests
Pests will miss 12% of time

It sounds like the perfect Kerria's debuff team. ATK wise, Kerria will end with 40+18+15+20+22 = +115% ATK, 10% skill damages and 15% damages. That's not awesome but still good for her.
Skill wise, it's a solid 1.2+1.2+1.36+1.2 = x1.96 skill rate, and she will reach almost 75% skill rate.
Debuff wise, it's a solid -70% ATK for pests with a -12% precision, added to the already 50% evasion of Kerria. White Tulip appears as a gift from gods here with 3 exellent abilities for Kerria's support.

The only two flaws of this teams are the low speed (really low speed) and Aconite since she is super hard to get for us.