aqua is one of the few remaining keyblade masters from her world, and has been trained to be a protector of the worlds since she was young. she is fiercely loyal, and can be rather quick to assume and judge others. she has two best friends who mean the world to her by the names of terra and ventus, and would do anything for them-- she's incredibly self-sacrificing even to a fault. she's recently entered cascata after a decade plus of isolation, and is not used to being around other people, and her emotions and sensory intake can often be a little overwhelming*. that being said, she is rather friendly and maternal, and will do everything she can to help a stranger in need.
*i do headcanon aqua with post-traumatic stress disorder after her time spent in the realm of darkness, she often wonders if she is hallucinating and has difficulty staying in the dark too long without some sort of light source (flashlight, phone, etc.)
aqua is quick to offer a helping hand and believes, like most kingdom hearts protagonists, that friendship is the strongest bond and can conquer all. she will most likely try and be your character's friend upon meeting them, however she can judge by appearances. once a character is her friend they can expect to have her unwavering loyalty and trust. her two best friends are terra and ven, fellow keybearers she was raised with, and she talks about them incessantly, and hopes to find them someday soon.
aqua has a bit of a judgemental attitude ingrained in her by master eraqus, her teacher. she does not like those who freely use dark powers and struggles to understand it. part of this also comes from her own self-loathing, as she has let loneliness, bitterness, and anger take over her during her isolation in the dark meridian, knowing those are traits that can welcome the darkness and evil in turn. i would like to see her become less prejudiced over time.
additionally, anyone that threatens her friends is in for a world of hurt and is unlikely to get back on her good side.
i personally headcanon aqua as bisexual (you know she grabbed cinderella's butt... don't lie to me) and out of her canon castmates i enjoy shipping her the most with terra, as i think their dynamic has the potential for a lot of chemistry. that said i don't mind her being shipped with others, it would require a lot of time and patience given that aqua can be rather oblivious to these sorts of things, so it would definitely fall under the 'slow burn' category.