How to beat this miserable fight on harder difficulties without pulling your hair out.
Strategy *slight CHAPTER 6 Spoilers*
Despite the game highlighting Franky and Robin as main targets to save I recommend you do them LAST because they have tough bosses in them. That means avoiding Ruby City and the Sea Prison. Also Usopp’s quest has a painful fight too so you might want to save that for later as well, so avoid Topaz Mine Town. Use all the other quests to get a stockpile of skill points to power up Luffy. Health Regen is useful for mistakes and the inevitable unlucky hits and Gum Gum Gatling is a must for this strategy.
With that out of the way, here’s how I managed to get through this cheesy boss with a cheesy tactic.
First you’ll need to be dodging right out of the gate as Tashigi and her cronies will instantly be attacking you. Once you get a second to breathe use ranged mode to try and headshot the Navy sailors while avoiding their shots and Tashigi’s attacks. Hopefully you’ll manage to stun them and do takedowns without taking too much damage.
After the soldiers are out of the way it’s time to focus on Tashigi. You may despair when you see how little damage she takes from your hit and be tempted to switch to armament haki but DON’T DO IT. It’s too slow and you’ll get slashed. The key is to use observation haki basic attacks AFTER Tashigi finishes an attack. Just mash X after she attacks and get the Gum Gum Gatling going and knock her down. What you can’t see is the stun building up and eventually after a knockdown Tashigi will take a knee (not like that) and be open for a takedown. The takedown will take a big chunk off of her health bar and then your only goal is to stay alive and get in enough hits to stun her again.
So that’s how you attack but how do you protec? Run around like a chicken with your head cut off while keeping the camera focused on Tashigi. Also be prepared to tap dodge if she goes into an iaido draw stance (stands still and puts hand on blade’s hilt). After a few moments Tashigi will dash forward and turn invisible to do a slash at the point you’re at. Learn the timing and when to dodge and you may also need to learn to dodge her cheesy jump attacks. Remember, after each attack is an opportunity to do an attack chain of your own. I don’t recommend attacking any other time but then because sometimes she decides she has super armor an retaliates if you attack first.
As far as I saw she doesn’t change her patterns much throughout the fight, she might get a little more aggressive when her HP is lower and she can do multiple invisible dash moves in a row. The strategy remains the same. With a little perseverance and a lot of luck you’ll finally make it through and your reward is Nico Robin.
TL:DR Run around and dodge attacks then do observation haki combos after she attacks to build stun and do takedowns.