Pygmy Water Lily is a solid choice since she gives 20% rate/25% damage crit boosts, extra blunt/pierce/magic weakness coverage for the squad, and an attack boost that gets as high as +45% if at least three attack types are covered naturally by the squad.

Swimsuit Sakura is a bit on the slow side (335 speed) but if you're looking solely for weakness and crit boosts she's another good choice, giving +20% to crit rate/damage, +15% weakness damage and extra slash/blunt/pierce weakness coverage for the squad that allows her to hit all four standard weaknesses just like Pygmy Lily.