Mitsuru is depicted as having a Cool, Calm, and Collected™ personality, accompanied by the popular Lady of War trope. Mitsuru, however, is much more than a simple trope.
Though she comes off as very suave and charismatic, Mitsuru is incredibly awkward in social situations. While she is incredibly wise for her age, she grew up in an environment that did not allow for much interaction with anyone her age. She wasn't really allowed to be a child--from a young age she was taught in a strict atmosphere so as to be taught in the ways of becoming the next heir of the Kirijo Group. Therefore, while she is capable of having mature and often serious "adult" dialogue, Mitsuru is unable to fully grasp how to have a normal conversation between friends or acquaintances. Her Social Link is a great example of this! Even when it comes to marriage, she always thinks of the business benefit of her actions, and often not of her own happiness or desires. This makes Mitsuru come off as somewhat cold, despite her best intentions. She sees logic is all situations, ascribing it as the number one priority when making decisions, not really taking into consideration many other factors, including her own or others' personal feelings. This doesn't make her a "bad person", but it does make her come off as rather manipulative and perhaps even selfish.
In her involvement with the Student Council as their president, she displays a remarkable amount of academic knowledge and charm, which perfectly shows off just why she was chosen as president by the student body. The students of Gekkoukan High seem to regard Mitsuru very highly, praising her for many traits, such as her academics, wit, charm, and charisma. Yukari and Junpei say it best before witnessing Mitsuru's speech.
Yukari: So, she did get elected. Well… I guess she IS the most popular girl in school. Junpei: You can say that again! There’s like some kinda aura around her…
After said speech, Junpei even remarks how he couldn't understand a word she was saying, and how only someone as popular as Mitsuru could pull of a speech like that and still be praised.
Despite being highly regarding by her peers however, Mitsuru doesn't really have a close relationship with any of her classmates. The only friendship she seems to have in the beginning of the game is with Akihiko, whom doesn't seem to have that deep of a connection to her at all, aside from being her comrade in arms. This ties in with her inability to hold a casual conversation--while everyone looks up to her, they are also incredibly intimidated by her. Similar to a relationship between a student and teacher, or even a mentor and their pupil. While there may be some kind of closeness there, it is not one of friendship or companionship, but one of admiration. Due to this inability to cultivate friendships, Mitsuru is incredibly lonely, having never learned how to rely on or talk to others. She is simply unable to because she never really learned how.
Mitsuru is also incredibly hard on herself, which is obviously due in part to her position in the Kirijo family, but also due in part to her lack of social interaction with people of her own age group. She is a perfectionist to the core; only expecting the very best of herself, and of others. Mitsuru is always sourly disappointed if the protagonist does not do well on their exams, but offers rewards if they place very well. She is most enthusiastic seeing others succeed, and busts out the French (or, in the Japanese version, her English) to comment on a job well done. "C'est magnifique!" she says, a smile on her face.
Perfectionism [per-fek-shuh-niz-uh m]
- Any of various doctrines holding that religious, moral, social, or political perfection is attainable.
- a personal standard, attitude, or philosophy that demands perfection and rejects anything less.
The random French thrown into her dialogue is also a part of Mitsuru's personality--she throws it into her speech quite regularly. One can assume learning the language was part of her education as an heir, or perhaps she learned it on the side on her own time. Was it a subject taught at Gekkoukan? Who knows! Either way, it's part of speech pattern, and while she never mutters anything too complex, it does baffle Junpei as to what she's saying sometimes.
The last part of personality I will touch on is her air of "badassery", if you will. During the first "official" SEES encounter with Shadows in Tartarus, Mitsuru rides in on her very own motorcycle, giving her an air of independence and "coolness". Because motorcycles are pretty radical. And cool. However--to no one's surprise--Mitsuru acts like owning one is no big deal, as it's great transportation during the Dark Hour. (Again we see: logic wins out!!!) It gives others the impression that she is truly independent and capable, and that she doesn't need to rely on others for anything, even transportation.
And that is Mitsuru's biggest flaw--her inability to rely on others and communicate her needs and desires properly. Despite all the growth she experiences during her time at Gekkoukan High and SEES, it is still a struggle for her, partly due to deep conditioning from her childhood in her role as heir to the Kirijo Group, and similarly her lack of [casual] communication with people her own age.