While Shindai-Rengoku might be the best, its basic counterpart, Shindai-Akuma, has a similar move to Tailed Spirit Counter, Samurai Sekiro. This move summons samurai spirits that deal a decent amount of damage. You could always just use every Xeno-Dokei ability off cooldown. I think using a companion is also a great way to get the boss off you while you use your abilities.