There is 3 6* counter no? Anemone, Helenium and Mistletoe. Two of them are Pierce (Anemone & Mistletoe).
Anemone seems a bit weaker but actually her abilities are a perfect combitation. Counter based on defense + 15% defense for all. Aside this, she also have one of the best skill type (if not the best) of the game. 3 random enemies attack. It's like a multi-target skill but dealing three time more damage if there is only one target.
She is just perfect to handle both normal pests fights, boss fights and event raid boss fights since she a really solid unit for counter teams.
I don't really like her in term of waifu power but she is one of the 6* I want the more for my squad.