PersonalityI would argue the most notable part of Mitsuru's personality is her strong sense of responsibility. She clearly feels responsible for anything relating to the Dark Hour, but this aspect applies to all areas of her life as well. Mitsuru is the Student Council President and thus takes on a number of extra responsibilities for the school. She is also the top of her class and is studying college-level material. She keeps on top of the other SEES members about studying and will not spend time with the protagonist unless he or she proves they hold the same level of commitment to academics. Clearly then, she takes her responsibility as a student very seriously. Further, after her father's death, Mitsuru takes on the responsibility of leading the Kirijo Group. Although she could back out of being in an influential position due to the number of people who longed for power in the group, she doesn't. Even in the face of being forced to marry an intolerable person and being unable to attend college to pursue something she would like, Mitsuru chooses to accept her responsibility. Having a strong sense of responsibility is certainly a good trait to have. However, Mitsuru is almost responsible to a fault. She is very quick to self-blame when anything goes wrong. She blames herself for all sorts of things ranging from "forcing" the members of SEES to join and fight, Shinjiro's Persona accidentally killing Ken's mom, Shinjiro's death, her father's death, being too trusting of Ikutsuki, not being able to ignore her own feelings... The list goes on. Mitsuru seems to feel as if she should have complete control over everything that happens. Therefore, if something bad occurs, it is immediately her fault for not foreseeing the outcome. Luckily, such feelings fade away with each new resolve.
Mitsuru's focus on all of her commitments and responsibilities makes her pretty reserved and professional. Unless it is a matter of business, she usually keeps to herself. She is perceived as being "icy" and aloof. In reality, though, she just has her hands full. She is too occupied with school, SEES and family responsibilities to be bothered with casual chitchat or typical friendship bonding activities. While I truly think Mitsuru would enjoy such idle time, she simply accepted her life has to be without others in order to fulfill her responsibilities. Being unable to befriend others was just another sacrifice that needed to be made. Further, Mitsuru seems to feel she has to take care of everything by herself. Although Mitsuru is certainly mature, calm and collected like she appears, she keeps her true emotions to herself because she feels she has to. Asking others for help would only be a burden or be too dangerous. Ultimately, though, Mitsuru does not trust others. That isn't to say she doesn't believe others can get the job done as well as she can. She just doesn't trust that anyone would want to help her. Almost every relationship in her life has been out of obligation, after all. Why would she believe someone would want to help her because they care about her? Mitsuru's father even points out her unwillingness to work together with others:
Takeharu: I’ve told you time and again; none of the blame is yours.
Takeharu: "Two in harmony surpasses one in perfection." That has been our guiding principle since the Kirijo Family separated from the Nanjo Group.
Takeharu: You must learn to trust in others, Mitsuru. There are things in this world that cannot be accomplished alone, no matter how many sacrifices you make.
Her father knows she doesn't want to burden others and therefore will make any sacrifices necessary in order to get things done alone. He also knows, however, "no man is an island." Everyone needs help and those who do not ask for it will eventually break. Despite her father's words, Mitsuru continues to carry the weight of the world on her shoulders by herself until she learns to ask for help. Once she does, Mitsuru finally understands the meaning of her family's guiding principle. All the sacrifices she made only got her so far. Once she came to rely on her friends, however, she was truly able to grow and succeed.
While Mitsuru certainly does not let others take care of her, she has a motherly and caring side herself. Mitsuru encourages the members of SEES to take care of themselves and not push themselves too hard. She reprimands Akihiko for treating fighting Shadows like a game because she feels if he does, he will get hurt. Mitsuru also keeps on top of them in regards to studying and meeting their other responsibilities like a good caregiver would. She doesn't want anything bad to happen to them. Her intentions don't always come across in the way she'd like them to, but her heart is certainly in the right place. For example, in a drama CD, Mitsuru signs the protagonist, Yukari, Junpei and Fuuka up for summer classes without asking them. Extra schooling is far from what any of them want during summer break, but Mitsuru did it as her way of looking out for them. She feels guilty the battle against Shadows has taken away from their studies and wishes to make up for that when possible. Lastly, keeping her own feelings and struggles to herself in order to not burden others is another example of her way of caring and looking out for them.
One last notable aspect of Mitsuru's character is her ignorance of the world. Growing up in a rich and powerful household denied her the opportunity to experience what most people go through. She certainly did not live a "normal" life by any means. Through her social link, the player comes to realize that Mitsuru has never experienced activities like eating ramen or other fast food, going to the movies or even having a friend to express her feelings and concerns to. Mitsuru is used to catering, expensive restaurants, maids and other luxuries provided by money. Therefore, while Mitsuru is usually confident, she becomes relatively awkward and uncomfortable in "casual" situations. She's been through so many formal and professional situations that she could attend a fancy CEO party with her eyes closed. Going to the movies or to get some fast food by herself? Not so much. This awkwardness is seen right from the beginning of her social link when Mitsuru whispers to the protagonist to ask what sort of etiquette exists for eating ramen. She knows she has no idea what to do in "casual" situations and seems to be dejected when she is reminded of this.
Mitsuru's ignorance of everyday situations may not seem like a big deal. However, it certainly plays a huge role in why she doesn't have close friends. Being from an important and rich family already makes others treat her differently. Not to mention Mitsuru is basically perfect in regards to academics, her sport of choice and looks. She seems well put together and mature. Clearly people admire and respect her, but they also consider her as someone who isn't "like them." She is unapproachable due to her preoccupation with her responsibilities and her ignorance of the world for those who aren't rich makes her even more un-relatable. It's hard enough to become close to someone without having a barrier between you due to the fact you are from two completely different worlds. Most people consider Mitsuru someone who they could never befriend (usually due to feeling inferior) and Mitsuru has no idea how to relate to others because she has a totally different life perspective. In the drama CDs New Moon and Full Moon, Mitsuru eventually comes to realize how her loneliness partially stems from being unable to understand others and vice versa.
Despite all the drawbacks and struggles that Mitsuru has, however, she always shines through with motivation and a strong will to be better and stronger. She gets knocked down hard and it takes her a while to get back on her feet, yes. But when she does, she is stronger than ever. She learns to share her burden and responsibility with others. She learns to ask for help when she needs it. She learns that other people do truly care about her. She comes to accept and love herself. After learning all of these things, Mitsuru finds the barrier between herself and others begins to be break down. She is then able to truly live with her head held up high alongside the people she cares about.