Alright, Digimon fic idea time. Let's start by saying that Daisuke was born a girl and has been best friends with Hikari since they were five. Now that's out of the way, Daisuke either has something of a condition or is just slightly unusual, as once she turned 9, she started to mature rapidly, not getting too much taller than typical, but her curves developed quickly, leading her to have much larger breasts and wider hips than anybody else her age. Further, neither her parents or older sister pay any attention to her, thus while her classmates and friends might notice, they don't have the experience needed to help her with her growing body.
As such, although she needs one, she doesn't even own a bra and doesn't have any pants/jeans/shorts that fit her, meaning she has to wear skirts. She was fairly athletic before, and still is to some degree, but not as much up until she turns 11 and becomes a Chosen Child. Hikari noticed her growing and is the one to develop a crush on Daisuke first; it's not until they begin their adventure together that she finally acts on it, though, getting the chance to see Daisuke in action.
Now it should be said that Daisuke gets a whole new outfit in the Digimon World, just like in the anime. In this case, it's a short sleeved half-shirt and mid-thigh length skirt complete with sports bra and spats (I believe the look I imagined is like... Karin? I want to say her name is? From Street Fighter). Needless to say, the first time Hikari sees her, she can't take her eyes off of her (though truth be told, neither can Takeru). Now for some reason, in the actual anime, neither Takeru nor Hikari... or really any of the older kids ever get new outfits just for going to the Digimon World, but I'm thinking that seeing Daisuke like this makes Hikari wish she had a new look so that maybe Daisuke would look her way (she already does, a little, but Hikari either doesn't know this, or doesn't think it's enough).
Wanting a new outfit actually makes it happen, though not until after she gets her Digivice upgraded and acquires the Digimental of Light. On her next trip, her clothes change to a white bodysuit seemingly made of latex, ending just above her elbows and knees and very tight, with the Crest of Light large on her back and small on her front; white boots reaching just below her knees with a one-inch heel finish the ensemble. Needless to say, Hikari is excited to see her new look, and is actually really happy with it since Daisuke couldn't take her eyes off of her when she saw her like that.
Shortly after they learn that Ken is the Digimon Kaiser, Hikari finally works up her courage and kisses Daisuke. While surprised, this spurs Daisuke to ask Hikari out, and they start dating. Not a whole lot changes from what goes on in the anime, but between episodes, Daisuke and Hikari are having dates and getting closer. Time spent in each others' rooms leads them to exploring each others' bodies; Hikari is actually a little embarrassed that she looks like a little girl compared to Daisuke, but Daisuke assures her that she actually likes her like this, and that she thinks the way her body developed so early makes her a freak. Hikari disabuses her of that thought and ensures her that she's very beautiful just as she is. They eventually take some of their dates in the Digimon World, and get to explore each other in their outfits; they find that a symbol they've never seen before is printed across the ass of Daisuke's spats (Crest of Miracles as seen on the top of the Digimental of Miracles and on Magnamon), and Daisuke finds it very fun to peel Hikari out of her bodysuit.
About when Ken is finally defeated, two things happen: Daisuke turns 12, and she has her first period. Hikari managed to help Daisuke not to freak out too much and get her what she needs. Daisuke starts growing body hair (armpit, leg, pubic), and decides to leave it, since she never learned how to shave it, and will keep it even after Hikari starts to do so and teaches her. They continue to get closer as the fighting intensifies, and then the final battle takes place. The world that can grant wishes makes Daisuke think, as only the week before Daisuke and Hikari had promised to stay together no matter what, and they both shared that if they could, though would love to have children together. Daisuke makes a wish just before the fighting is pushed into the Digimon World that she would be able to have a child with Hikari somehow, and suddenly has a tingle flow through her, and a bright golden glow surrounds her. As she's in her Digimon World outfit, the Crest of Miracles is plainly visible on her abdomen right below her navel; it will remain there like a tattoo from then on.
Daisuke was due to have her period the following week, but it never arrives. In all the excitement, though, she forgets it's supposed to have come, and it's not until another month later that she realizes it. When she starts having all of the other symptoms, she tells Hikari what she suspects, and they manage to get their hands on a test to confirm it: Daisuke is pregnant. At first, Daisuke panics, and Hikari asks if she's been cheating on her with a boy, which Daisuke vehemently denies; in fact, Daisuke is pretty disgusted that Hikari would ask her that. So then it comes down to how it could have happened, which causes Daisuke to recall their conversation and what happened in the Wish World. That's when Daisuke lifts her shirt and they both see the Crest of Miracles there. While it doesn't clear Hikari of all of her doubt, she does agree that it's possible.
Unsure whether Daisuke will attempt to hide it or not, or if that will even work, but she does carry to term, and her previous development makes the delivery easier than anyone who just turned 13 should have. Once she does deliver, her parents finally wake up to what they should have been seeing all this time and make Daisuke get the DNA of her new daughter tested. They can definitely match half of the genetics to Daisuke, but testing against all of her male friends shows no full matches (though Taichi shows a distant match, meaning a family member of his could be the full match), making them think she was raped. Finally, Hikari finds a way to discreetly get her DNA tested against the child, and they find a match for the other half of her genetics, proving to Hikari that it was just like Daisuke said, and that this was her daughter, too.
From there, maybe an epilogue where they are still together, perhaps not married, but raising their child together. Possibly having them discover how to activate the Crest on Daisuke which will allow them to have more children together. Disregarding tri, or possibly making it so that some of it is averted since Daisuke is very different to the official anime.
I think that's all I have for it. It's really more fleshed out than I thought, probably because I wasn't able to write it out at first. It's really a pretty interesting story, and it averts some of the more annoying things, like the competition between Daisuke and Takeru. Now could I write this? Not until I do some more research, which I've been meaning to do for quite some time now. But yeah, that's all for now...