Tashigi is a supporting protagonist of my Grand Line arc. In her canon, she was a swordswoman and a speedster, who often bit off more than she could chew. Here she is more successful and powerful, having all six basic Rokushiki, but she is still overconfident. Whom can she beat in a fair fight?
Can: Princess Avyanna
Avyanna is the princess of the Kallanians, and yet another wasted female warrior I buffed. She wields a purple laser cutlass, which she is quite skilled at using, even though she has no supernatural powers. She also has daggers and a blaster, so all her attacks produce heat, so the Tekkai is worse than useless. But Tashigi does not need the Iron Body, for she has the rest of the Six Powers and is much faster than Avyanna. It's Tashigi's Haki that makes a difference, because she can sense all attacks coming with Observation, and ensure lightsabers won't cut her sword with her Armament, so her superior skill can overwhelm Avyanna.
Can't: Charlotte Smoothie
Tashigi has fought Smoothie and managed to defeat her before, but she had the help of Kitty, Virago and Pan, and Smoothie had fought a gigantic mechanical kraken earlier. In a straight fight, few characters present in the story can beat Smoothie in a duel, and that's because she has Armament and Observation above Tashigi's, and she is also an even more skilled swordswoman. While Tashigi can avoid being grabbed instantly with Soru and will land a few hits, she is simply not strong and skilled enough for Smoothie, who can juice her instantly once she has her in her grasp.
Can: Ah'tilla
Ah'tilla, the vicious Yuuzhan Vong Supreme Commander, was a powerful Jedi killer, who could not be affected by anything related to the Force. His big advantage against Tashigi is that he is immune to her Observation Haki, as well as the fact his bioelectric amphistaff can do some serious damage to her. Finally, the Plasma Eels and Blast Bugs can hurt Tashigi from long distance. Yet, while Tashigi will definitely struggle, she can still win. She can skywalk, meaning she has the aerial advantage, and she can also use her Tempest Kick from long range. Her Soru ensures she is much, much faster than him, and her Armament Haki can allow her to block the amphistaff and do severe damage to him. As long as she doesn't make mistakes, she stands a chance.
Can't: Force Hunter
The Force Hunters are very tough enemies. So far, only Pan has defeated one on his own. They have the immunity to the Force and Observation Haki, but also counter Tashigi's fighting style very well. She is a melee fighter that uses a sword, which means she will be close to the Hunter and its double chainsaw. Apart from the Hunter being physically stronger, it can fire bullets and homing missiles that catch up to her speed, use its jetpack to fly and counter her skywalk, and employ a regenerative energy shield that can stop hits, even from Armament Haki, swords and the Finger Pistol. Tashigi doesn't stand a chance.
Can: The Silver Werewolf
Tashigi is incredibly fast, but can she deal with beasts that stand out among speedsters? The answer is yes. She can also run faster than the human eye can see, but will have an easier time against this beast than Leah had, because she is not weak to silver. While the werewolf is strong enough to make her struggle, she still can track his movements with her Observation Haki and catch up with Soru. Also, the monster is not fully sapient, so Tashigi is smarter. Hit and run tactics will give her the victory unless she slips up.
Can't: Biomeka
Biomeka might be slower, nearly stationary compared to Tashigi, but he has an advantage at everything else compared to her. Her glasses may or may not save her from his stone gaze, which is incredibly powerful, while his armor is nearly impenetrable and will need exceptional Haki to break. She only has basic Haki, so she will not be able to break the armor easily. Biomeka will swarm her with turrets, use fire that deals with Iron Body, easily shrug off normal sword slashes and the Finger Pistol, and in the tiny chance he dies, his rage allows him to become a fiery mobile sword demon and finish her off.
Can: Rhymey Ward
This might be controversial for some of the readers. How can she beat a Starfleet pony, and the swordsman to boot, since he was essentially the final challenge of an arc? Well... sure, he is a very skilled swordsman, can fly, both of them call their special attacks and can infuse their sword with energy, and finally the heat of Rhymey's hot gust of wind will make Iron Body problematic. However, Tashigi still has some advantages. She can use her Iron Body to stop his Drill Quill, she can cut through steel with a special technique, and even though he can make his sword anew if it's broken, that only mitigates her advantage. She also can use Rokushiki to counter his physical strength, and overall shares his strengths and weaknesses. Except she also has Observation Haki that senses his movements, while he needs his visor to do so, and her Armament Haki can damage it. Also, her Ranga Cho is too fast for him. It is a close fight, but Tashigi has the advantage.
Can't: Jack the Drought
Jack the Drought is a Yonko Commander, and of Kaido's no less. She is faster and probably smarter than him, so she can land hits, but Jack can take a serious beating. He is much, much stronger than Tashigi, both in terms of brute force and in terms of Haki, so he will need few hits to actually win. He has picked fights with the likes of Tsuru and Sengoku at the same time and managed to last relatively long in canon, and also fought Finn and Leah at once in Stormwolf. His mammoth form is a big target, but also above anything Tashigi has, and if he freezes her with his Glacial Stream, she is done for.
Can: Mezuki
Mezuki is one of the Two Tormentors, and a powerful Yokai. He is a large warrior and a swordsman who can fire Spectral Bolts. His horns can also gore Tashigi. However, a Season 1 Finn was fast enough to react to Mezuki, and Tashigi is even faster than him. She can land many hits on him, and while he can endure a beating, her Haki can increase the damage output a lot. She just has to play defensive.
Can't: Rey
Tashigi and Rey look similar at first. Both want to be strong and independent, both can skywalk, both are swordswomen, and both can sense their surroundings, Rey with the Force and Tashigi with her Haki. But while Tashigi's Armament Haki can save her sword from being bisected, her Haki is not exceptional. On the other hand, Rey's Force powers stand out compared to everyone else. She can Force Push Tashigi away, Force Choke her, strike her with lightning or pull her closer for a strong saber slash. Her lightsaber is also double and can cut through Iron Body. In short, Tashigi has a serious disadvantage.