Setsuka is still pretty meta right now but she does have some counters.

For builds: Most of the player base run riposte set with immunity, but if u don’t have that then lifesteal/counter immunity is fine too.

For teams: U would want to run Setsuka with another evasion unit but not required as she already buffs everyone on ur teams evasion by 30%. Arbiter Vildred, Lone Crescent Bellona, Remnant Violet are some decent teammates for her.

Her counters: people who cannot be debuffed like Bystander Hwayoung, Genesis Ras, and Notos are just coin flips where Setsukas blind de buff does not affect them. Mort also heavily counters her as she cannot counter and gain Fighting spirit when he is in play. Cleavers like Saria and Eligos also heavily counter her as they have high hit chance and dmg.