Who is this, I don’t remember her?
This is Strea, she's the first "SAO Gameverse AU" Heroine to be introduced in the aforementioned SAO AU: Is basically an alternative universe comprised of videogames (With each one acting as a new 'arc' would for the AU) that splits from Canon SAO during the end of the Aincrad Arc, where a giant glitch interrupts the duel between Kirito and Kayaba letting the former 'win' the fight, but somehow the game doesn't end, leaving Kirito, Asuna, and the rest of the Clearers trapped in Floor 76+ and with no other option but to go to try and clear the game all the way to Floor 100 as originally planned. It then goes on to introduce the rest of the main canon cast earlier through plot-convenient shenanigans (For both Leafa and Sinon to end up in SAO and both Liz and Silica went up trying to see if Asuna/Kirito were okay respectively only to end up trapped there too), and all new heroines with each arc/game, both with original plots and parallels to some of the canon ones.
Hilariously, it started out as a fanservice-based cashgrab, as you can see with the design of Strea-chan above, she's basically firmly a 'Hentai'-bodied heroine thanks to that Beta Avatar she's possessing, with tits canonically 6 or 7 cm. bigger than Suguha's, comparable to Kirito's head as we see in the CG above (And as ass the size of Sugu's tits, lol), plus her personality being basically extremely flirty, no boundaries, very fanservice-prone, low common sense kinda girl trying to promote the harem shenanigans canon SAO doesn't actually have despite the haters saying otherwise. However, somehow despite embracing firmly all the things the haters say make Canon SAO suck (Despite not actually having), it somehow went on to give al the girls more and better character development than Canon ever did (Both as a group of friends, which canon practically never does onscreen, and individually with Kirito). The latter games also honestly had main plots comparable if not outright better than most of Canon SAO's arcs, the heavy harem fanservice honestly was just a bonus because somehow it really made SAO's plot and main cast way more enjoyable and developed than Canon ever managed, I personally like it way more than Canon XP
As for the 'joke' I made, this is because Strea's true identity is actually an AI, "MHCP-002". Just like how Yui is Mental Health Counseling Program 001, the first game, Hollow Fragment, revealed there were a bunch of others, so Strea is in a bizarre way her 'little sis'. Strea managed to escape thanks to the glitch that caused the split in the timeline and like her 'sister' program before her she fixated on Kirito...only that unlike Yui what she wants with Kirito is not family-friendly at all, unless you count incest hentai lol-