Anyone else finds it very weird that we never got any kind of backstory for Tashigi?
She's someone we've known since chapter 96, who's been in multiple story arcs, yet her past is a total mystery. Oda has created a backstory for basically every other character that has the same level of importance as her (I'm thinking of characters that are not as prominent as Nami or Vivi but are not as secondary as, for example, Marguerite or Tristan either).
If we look at Koala, Pudding, Reiju, Carrot, Perona, Rebecca, Hiyori, Hina (just to name female characters)... we know at least something about their past, about what they did before we met them in the story. For some of them we even got entire flashbacks, for others Oda provided information in SBS or other canon material. For many secondary characters, their past can be easily inferred from the context. But for Tashigi we have *crickets chirping*.
We only got that drawing of her as a child that only tells us that she already loved swords and wore glasses. She is also notably absent from the Marine spread Oda drew for Film Z, though the reason for that could be that she's too young and wasn't there in Z's time.
I don't believe Oda has never thought of any backstory for her. How she got interested in swords, where her dream comes from, how and why she joined the Marines, how she met Smoker... Oda is an author who always crafts his characters with care, so he must have thought of at least a shred of backstory for Tashigi. I think that for some reason he just never made it public– despite fans probably having asked him about it throughout the years, like with Kid and Killer's backstory that he revealed by answering a fan letter.
I think there could be two reasons for Oda not revealing Tashigi's past (besides not having thought of one in 22 years, which I doubt):
1) Her past is important and will tie into significant story developments that are yet to be revealed. It could be something connected to Kuina. Maybe she's Kuina's sister/cousin/distant relative; maybe her existence played a part in Kuina's death; maybe she knows something important due to her connection to the Shimotsuki clan... there are many possibilities.
2) Oda is waiting for the right moment to tell us Tashigi's story when it would make the most sense for her character. This moment could be, for example, when she and Smoker decide to go against the World Government once and for all and openly support the Straw Hats in the final war. In that moment, a flashback containing new information would make us better understand why they're ultimately making that choice. Maybe that moment was supposed to come much earlier but then, as we know, the story ended up being much longer than what Oda had originally planned so we're still waiting.