Ok, I know next to nothing about kos-mo. Can a fan of the character please tell me why she would be picked over any other character in the Xeno series, especially over Elma or Rex? From what I get shes a side character that has appeared in a lot of the Xeno games, but is mostly either a side character or cameo. Why her?
She isn't a side character, she's the face of the franchise. They even put her front and center on their
20th Anniversary Commemorative Website. (Fun fact: Naughty Dog couldn't even put Crash Bandicoot on their anniversary celebration because of Activision. I mentioned this to give you an idea of how close and interchangeable she is with both companies involved.)
Out of any Xeno character, including Shulk, KOS-MOS is used in crossovers/promotional materials the most. Both Bandai Namco and Monolith Soft love her, and - design, personality, plot, or some combination of all of the above - she's the inspiration for many of the characters we know and love today like Fiora and Elma.
Interestingly enough, most of her cameos are implied as canon appearances because of interdimensional travel shenanigans. Thus, she's lived on past her initial PS2 appearances.
Does she have some badass moveset potential or something im not seeing?
She is a self-classified annihilation weapon, so her moveset potential is totally bonkers. She has handguns, lasers, hammers, bows, drills, energy wings, gatling guns, shoulder mounted rail cannons, etc. Not only can she morph parts of her body into them because of nanomachines, but she can also summon them from literal hammerspace, and then have more fitted on to her. There's a reason people buy her
figurines like hotcakes (just look at all of those accessories! That's not even half of it) because she's a one woman army. It's easier to show than tell, so take a look yourself:
