I will spoiler tag each answer but I'll post which answers give you Xion, in case you want to know haha! As well as my reasoning for each one.
A lot of my shyer friends got her.
Her Disney movie
The Hunchback of Notre Dame. I largely chose each Disney movie based on the protagonist (usually peoples' favorite disney movie is because of some connection with a main character). Quasimodo is largely a victim of his surroundings and is treated as if he isn't supposed to exist and must be hidden away from having a true life. As such he's grown up quite shy and gentle-natured, and he yearns for a normal life he can't yet have. This one almost went to Roxas, but I thought Jim from Treasure Planet was a better personality match.
Her Flower
The Dark Succulent. This portion was largely based on color/shape association. Not only does the plant suit her darker aesthetic, but succulents are known for being easy to care for, which I think matches Xion's severely low standards of just wanting to be remembered and to be allowed friendship.
Her Grades
Good except for participation. This was again geared for the more quiet/shy folks. I think Xion would be quite good in school as she seems to be a smart girl, but her participation grade would likely suffer.
Her Song
The Place Where the Lost Things Go, from Mary Poppins. Not only is it a Disney song which is always a bonus, the lyrics describe the situation with Xion and her friends so well.
"Memories you've shed
Gone for good you feared
They're all around you still
Though they've disappeared
Nothing's really left
Or lost without a trace
Nothing's gone forever
Only out of place"
It almost sounds like Xion trying to comfort her friends
Her Animal
The Butterfly! Admittedly, there was little reasoning behind this other than the fact that it just felt right. I couldn't think of any other animal for her. I didn't feel like a doe encapsulated her beauty. I think part of it may have to do with the sentiment of change/metamorphosis, or the butterfly effect. How Xion was able to effect so many people, to the extent that their hearts never truly forgot her (Axel and his extra sea salt ice cream).
Her High School Persona
Invisible, of course. I don't feel that one particularly needs explaining.
Her Ride
The Prince Charming Regal Carousel! I had difficulty imagining Xion enjoying any of the fast paced thrill rides like her friends. I think she would enjoy something beautiful, with a nice view. It was a close choice between this ride and Soarin'.
Her Vice
For her worst vice, I picked secrecy. I think that a lot of people who would relate to Xion would probably struggle with holding in how they truly feel. That can really damage oneself and result in harm to other people.
Her Quote
The quote is "Thank you for calling out my name...thank you for letting me be your friend." Have
this clip from the KH Orchestra in case you want to cry.
I think Xion is very common because most KH fans/game nerds are some degree of introverted. This means the most likely characters to get are Xion, Ventus (he's not terribly shy, but moreso than Sora for certain), and Riku.
Genuinely, I'm surprised I haven't seen more Aquas!
If anyone is curious about the other characters just ask! I remember everything I chose and why quite well, particularly so for my sea salt babies <3