Aqua. Just saying that name stresses me out. You might be wondering what could cause that statement, and the answer is quite complex.
Well first thing's first, despite her name she didn't have water powers (kinda sucks not gonna lie), just the typical fire-based ones that Blaze has. She was also not a princess like her prime counterpart, in fact pretty much just a regular person in terms of background. The reason for this is simple; the "Sol Empire" was simply in the same dimension and universe as Moebius and also wasn't anything of the sort; instead it was a "Sol Republic", featuring a democratically elected president, and in its history there was never the rise of a nobility, the Sol Emeralds were simply guarded by the Military rather than a monarch like with the Sol Empire. Thus after, what, some hundreds of years? Aqua is basically the only person from her family who ever had taken a position of power there.
Lack of heraldry and vague allusions to the Sol Republic's system of government aside, she was a rather anxious fellow, seemingly overwhelmed by just about anything, compared to Blaze who seems much calmer and more stern about things. Despite this, Aqua was persistent and kept going along despite the struggles she was having there, what with the micromanagement of a entire country. She kind of falls into the same category as Sparkles and O'Nux where she wasn't as, err, morally compromised or inverted like most other moebians, but comparatively she was surprisingly not pacifistic either. Despite it adding more to her load, she was in fact not as complacent (seriously - that guy almost intentionally let Demon Island fall to us), she would take action if something was wrong. It did take its toll on her mentally however, especially when she had to hold the Kingdom of Acorn (and thereby, the Suppression Squad / Anti-Freedom Fighters) from taking over Moebius. She was growing a bit weary and tired by the end of it all, just a lot of bitterness and anger at what we were doing and going to do to Moebius.
This brings us to some specific things she did. Basically, if you remember Kintobor - Eggman's timid counterpart trying to protect Moebius from our...mayhem. Just mayhem - she was that whole thing secretly helping him in many ways, allowing him to hide within the Republic, giving him things he needed to counteract us, even directly assisting and collaborating with him, and just generally sabotaging the Kingdom of Acorn. Tensions raised because we knew very damn well what she was doing, it was quite obvious from her public rhetoric and tone, and just certain things that there are no ways he could of done it alone (at least at that time). For all intents and purposes that made her one of the greatest thorns in our side. When Scourge came back from Mobius Prime, humiliated and wanting to distance himself from it by conquering the perceived-stagnant Moebius and creating a whole new "Moebian" identity, pretty much, we went and swooped up every other country, government, faction, groups, lands and whatnot in opposition (eventually even backstabbing allies but this is a whole other topic for later), but she kept persisting. Despite everything going terribly, as everyone else kept getting swept away with us becoming more and more powerful, there was just no surrender from her. The damned Republic was near impossible to actually invade, mostly just us beating them back every time they tried to attack or do anything against us or defend other countries and people, and by the end basically stood alone when we finally had the ability to take them over. It was frustrating to even deal with her lot and their shenanigans, especially whenever they actually did successfully stop us.
Even though she technically wasn't allowed to, in her last known moments she actually gathered the Sol Emeralds to fight Scourge who had the Anarchy Beryls (Chaos Emerald equivalent). The resulting fight was very brutal (but also would be very awesome if you saw it), although frankly I don't seem to recall how it ends since it dragged on from location to location and I couldn't keep up. Mainly just that there was this huge flash of light and Scourge coming by later, de-transformed from the Super form, stating that she had apparently scattered the Sol Emeralds across the universe so that we didn't just have two sets of emeralds basically (likely seeing a danger and probably knowing we would of wanted to have them in our posession), although he was always vague about what happened to her whenever it got brought up later on, only saying things like "I think she may of escaped", asking why we asked / cared, and other flowery statements of this sort, generally being dismissive (sometimes in mopey ways) on the subject. I can't tell if that's because that's all there is to it, if he did something, if she was dead or alive, or what but it's a strange ending to be sure, and the vagueness only keeps me curious. Frankly I wouldn't doubt any case as to Aqua's fate, good or bad, if there was something conclusive about her whereabouts but Scourge is very clearly unreliable here - typical of him if I'm being honest.
I don't really think she looked much different from Blaze, just didn't have the ponytail on her head (she kept it down instead) and often more squeamish and concerned expressions on her face. She might of dressed slightly more casually as well, probably from not having a lavish personal life. I would probably ask canonmates about these things if there were any, but there are obviously none, and I think the oddity of this not only being future life based, but also something niche like Moebius with non-canon / unofficial elements suggests I'm not going to meet any of them here in this life nor am supposed to.