General: Health must stay above 50% unless stated otherwise.
Satsuki 2b: Health threshold is lowered to 30%. You must initiate Bloody Valor (the RPS minigame) at least once.
Satsuke 3: If you're struggling with this fight, try targeting Ryuko first.
Satsuki 9a: If you're struggling with this fight, try targeting Nui.
Satsuki 9b: Use your break attack (B button on Switch controller) to break Ragyo's guard. Mind your distance and wait for openings; she does a lot of damage. While this is not required to S-rank this fight, it's recommended to initiate Bloody Valor against Ragyo for the Expect Nothing Less achievement. Due to her ridiculous HP pool her AI expects you to want to try to do damage against her, so if you try to heal during Bloody Valor (particularly when you're already at high HP), it should work against her all three times.
Satsuki 10: You must reach full valor and defeat the Primordial Life Fiber with your secret art. You can't build valor in this fight with RPS (thank god), you just need to use three special attacks in a row. After that's done, just make sure you don't kill the baby before your meter's fully built up. This is also required for the Here's My Sunday Best achievement.
Ryuko 1: Do not skip the cutscenes between fights; there are reports of it causing your time rating to lock at D.
Ryuko 2: Spam special attacks until it dies.
Ryuko 5b: Health threshold is lowered to 30%. You must kill Nui with the scissor blade (the purple sword) last and with a special attack. Focus on offense here; this has the toughest offense requirement by far.
Ryuko 6: If you're struggling with this fight, try targeting Nui.
Ryuko 7b: If you didn't get full valor against Ragyo in Satsuki 9b, you can try again here.
Ryuko 8: Do not sweat the time requirement here, it's more generous than you think it is. Spam specials whenever you have the chance.
Ryuko 10: You must defeat Satsuki with a secret art. This is also required for the Here's My Sunday Best achievement.