You must be a big fan of that Tashigi girl.
We saw the body http://www.mangahere.com/manga/one_piece/v01/c005/16.html . Or are you saying it's a double? And Kuina being a kind and sensitive girl because she cried once? You really are pushing this idea too far. Do you have a good reason to believe Tashigi is Kuina aside of her sexism?
It is indeed a body but its proven that Vegapunk can duplicate one. It would be interesting if Oda reveals that Vegapunk and her go way back. Its plausible that she is taking the kids to see him.
Crying is a way to release anything that you are not willing to show or holding back about yourself. Therefore, by crying she shows her real self and is not hypocritical and she is indeed a very sweet and sensitive girl about what other people think of her like Tashigi . Zoro and Kuina pretty much confess their pain and frustation to each other.
Other reasons:
- Tashigi coincidentally seems to like the Wado ichimonji (heck she is the one that actually introduces the name of the sword in the manga). I know she is a sword geek but when she fought Zoro she declared that she was gonna take Kuina's sword (not the yubarashi or Kitetsu). When Zoro defeats her (in the exact way that Kuina won the 2001 match) he declares that he can never give this sword. Therefore, she is actually more obsessed about the sword that coincidentally belonged to Kuina. Somehow, Tashigi has the exact same taste in swords as Kuina as well.
- In chapter 0 and the anime, we are introduced to the subpot that Koshiro believed that a girl would not be able to inherit the dojo or be a good teacher but her mom say that she is gonna be ok (the dscussion happens at the exact place where Kuina and Zoro made their promise) . What do you know ? Chapter 580 shows that Tashigi is an excellent teacher (Coby is really into it). We know damn well that Kuina would have proved her father wrong again (he sorta admitted that she was on her way to realize her dream). This subplot needs to be resolved as well.
- Oda could have just killed any theories by saying that both girls were born in a different year but no. I know there is the possibility of a twin but heck it would be too obvious and logical for Oda's standards (Ace's revelation).
- People say that she is not as talented as Kuina. Heck no, I mean she is reintroduced by using the same deflecting technique that Mihawk used(instead of cutting it she choses to change its trajectory). I mean we have never seen such dexterity except from Mihawk himself. If Kuina were alive, I would not expect anything less from her. I think her sexism bs pretty much stalls her progress and training.
The hilarious thing is that Oda denies that they are the same person (there is no relationship because they are the same) but everything he does suggest the opposite. It would be hilarious if she is indeed Kuina cause her haters would look beyond dumb cause they were pretty much hating on what motivated Zoro to be so awesome and fearless.