Ayame

Until they introduce a unit with Passive Lock, Ayame is going to be your primary go-to anti-buffing unit. Since the advent of Homura absolutely cucking Yuui out of her cut, Ayame's being a passive means she isn't inhibited by some pesky unique buff. In addition she gets (tries) to jack buffs off the target she slaps. Not only does her S2 hit hard with a high multiplier, add-on to that any potential attack buff or crit damage buff, she will more than likely kill the target (laughs in Victoria). Adversely this can also mean she jacks defensive type buffs as well off targets to make them more vulnerable. Only major downside is that while not exactly easy, it's not really that hard to build around her, as her S2 target's the unit with the highest attack. Ironically with Ayame's release, Homura fell off pretty hard, allowing for a double Ayame/Yuui offense cut.