ArcanaPersona 3 makes use of the thirteen Major Arcana of tarot cards. Each Persona user in the game represents a different arcana, which is in turn symbolic of their personality. Mitsuru's arcana is the Empress in all versions of the game. The Empress is associated with mothering and is the archetype of feminine power. Mitsuru is very mature and looks very feminine from her hair to the way she dresses. Additionally, I would argue she has definitely taken on a motherly role for the rest of SEES because she takes full responsibility for them, stays on top of them about their studies and taking care of themselves and tries to be the sturdy rock for the group to rely on. The Empress is also representative of abundance, material prosperity and power. It can represent coming from a background of being taken care of by your family and not having to worry about day-to-day affairs. Being the only daughter of the head of the Kirijo family, Mitsuru certainly has plenty of material items, money and power. Her dorm room looks like a second lounge, she wears expensive clothing and has maids and a personal stylist at home. Additionally, Mitsuru sometimes acts in ways that would suggest she grew up in a sheltered environment in regards to wealth. For example, she happens to walk by Junpei's dorm room in which the door is slightly open. Seeing that the room was a disaster inside and Junpei was nowhere to be found, she automatically assumes someone broke in and went through all of his stuff. Mitsuru is later embarrassed to have called the police when Junpei returns safely saying his room always looks that messy. Mitsuru wouldn't have ever imagined a room would be that messy by choice.
The Empress is known for her beauty and sexuality, as well as being mysterious and an object of desire. She can also be superficial. Mitsuru is certainly beautiful and admired by many. Further, based on her various Tartarus costumes as well as her design in Persona 4 Arena, I would argue Mitsuru is supposed to be an object of desire for players. I mean, this image and this image say it all. The other female characters are a bit sexualized as well, but I have seen more fans and official things accenting her breasts and butt compared to the others. Again, femininity, maturity and motherhood are all representative of the Empress, so it is not surprising that Mitsuru would be the one latched onto for this. As for being mysterious and superficial, Mitsuru really keeps to herself. She isn't superficial in a vain sense, but rather because she is just very reserved. She keeps everything at a professional level for the most part and deals with worries and her feelings alone. She comes off as being perfect, but no one is truly perfect. There is therefore some mystery in regards to her true self.
Lastly, the Empress can also represent the demands of the real world and life asserting itself through attempts to master it. Mitsuru is usually the realist of the group and reminds them to keep on top of life's demands other than being a member of SEES. In that sense, she is a reminder of life's demands for the other members. Mitsuru also tries to emulate perfection in every part of her life--tries to have mastery over it. However, she realizes at multiple points in the game that she can't control everything in life. Not everything can be calculated or prevented and it isn't her job to know exactly what will happen all the time. Only when Mitsuru realizes this does Penthesilea give rise to Artemisia.