Personality:

Mitsuki comes across as cool, indifferent, and distant with the aura of someone from high society on first impression (what kind of person makes a habit of addressing other people by their full name, even when they're already familiar with one another). Considering that her heritage is of the head family of a prestigious and longstanding clan, it isn't too surprising that she became the person she is today. What with the duties she'd have to uphold and the reputation she’d be responsible for, there wasn't much room to become anything else. At first shown to keep mostly to herself, she is often found in the literary club's room (which has only a handful of members) or the rooftop in solitude; she doesn't seem to have many friends — or any, for that matter. Mitsuki speaks bluntly to most, has a sharp tongue, and teases the people she's more familiar with to the point of being considered sadistic, yet still manages to seem refined all the while (sometimes even retaining a polite edge). All the same, she keeps a barrier around her to prevent people from getting close.

"Remember this: so long as we're Spirit World Warriors we'll always be alone."
— Nase Izumi to Nase Mitsuki, during an episode three flashback.

In the short Oniichan Dai~suki where we're given a peek at the Nase siblings' childhood, we learn that her familial relationships hadn't always been so frosty and that they all used to get along fairly well, openly showing affection to one another. While she still highly looks up to both Izumi and Hiro'omi in the present, the difference is that she used to outright exclaim how cool and amazing they were, and Izumi herself used to have a gentler demeanour. Somewhere along the line Izumi hardened, most likely when she took up the mantle of being the representative of the Nase clan, and began to be stricter on Mitsuki's learning. As a child Mitsuki was impressionable; adding to the fact that her sister was her role model, much of what she was taught by her ended up shaping the foundation of her character.

Mitsuki's later childhood was devoid of what most childhoods were supposed to have — she didn't socialise much in school, didn't hang out with others even when prompted to, and had never actually gone to a festival with her classmates until recently in the timeline despite really wanting to. It wasn't as if her sister restricted her explicitly from doing so, but because of the mentality that she'd be alone no matter what as a Spirit World Warrior, she simply didn't. It goes to show the extents of her self-control, even at her young age. Despite her firm upbringing, however, Mitsuki was babied by both siblings; whenever something potentially dangerous was going on she'd often be left in the dark or kept at home so that she could "watch the house", her only real way of gaining information being through her brother or other Nase clan resources (though her network seems to be much narrower than her brother's already limited one).

Nase Mitsuki is very much a side character in spite of how proud she may seem (she runs the literary club with an iron fist, her leadership jokingly compared to that of a dictatorship) and follows what her siblings say without any hesitation (except maybe a retort to her brother, though that would really be it). It's only when she meets Kuriyama Mirai (who is likely her first friend) and establishes a closer relationship to Kanbara Akihito that she begins to finally step out of her sister's shadow and the sidelines, developing her own sense of what is right.

In the beginning of the series she tells Kanbara Akihito to beware of Kuriyama Mirai, because the circumstance in which she transferred is suspicious (from her own intuition and sources). Some way or another, Mirai doesn't just grow on Akihito, but her as well. It's not quite explained what draws her to the other girl, but Mitsuki is noticeably softer on her, kinder, acting like an actual upperclassman and club president when she helps her find her way in a new city and accepts her into the club without much second thought. Though her interactions with Mirai can be rather stiff at times (no doubt thanks to her lack of friends until now), she still teases Mirai where she can, has no qualms against later tricking her into taking gravure shots (for a literary club issue that she wanted to publish in the drama CD), and cares about her quite a bit, worrying about her mental state when she finds out that Mirai was the one tasked to kill Akihito all along.

"…Aren't we friends, Mitsuki?"
"I'm sorry, what was that? Please speak up a bit."
"Aren't we friends, Mitsuki!?"
"Calm down, Akihito. Control yourself. Loud conversations are frowned upon in the cafeteria."
— Kanbara Akihito and Nase Mitsuki, an interaction during volume one, chapter one of the light novel.

Kanbara Akihito is someone who she was assigned to watch and guard, and someone who once nearly killed her brother. As often as they are in each other's company (along with the fact that they've known each other for a little over a year), Mitsuki doesn't see Akihito as an actual friend despite the latter describing their relationship as something close in one of his monologues. As aforementioned, however, throughout the series their relationship ends up evolving into an actual mutual friendship (the addition of Mirai makes for more animated conversations in the club room when normally it'd be dead silent aside from quips here and there and the occasional teasing to fluster him — what about the confession you were planning to make to me when we graduate? when spoilers, there is no confession) and we can see that Mitsuki isn't as cold as she appears to be. She's just awkward. Instances of her concern for him are when she calls Hiro'omi for the first time in a long while to check up on him after she's told him of the Hollow Shadow (she knows him well enough to understand that he would go and do something incredibly stupid) and when Akihito wakes up from his coma after months in episode ten. For all the times she's called him a disgusting pervert and told him to die she runs up to him and looks like she's about to hug him before he stops her. It's evident that she doesn't actually wish for his death — he's just a giant ball of trouble that constantly brings on migraines. Her words are harsh, but most of the time she doesn't mean them. Even her character profile on the official site states the following: "At first, she spent time with Akihito in order to keep an eye on him, but now, she really does care about him."

It's initially because of Mirai that she begins to advance her character, going to the festival that she once prohibited herself from and begins to open up to actually having friends. After that, it's through her friendships with both Mirai and Akihito that she starts to become more proactive. From the time she obediently stayed home during the Hollow Shadow to the time when she put her foot down to actively help despite Hiro’omi’s protests when it came to Beyond the Boundary, she's come a long way. The highlight of her development comes in episode twelve, when she pushes her brother to catch up with Izumi while she takes care of the barrier surrounding her fight with Fujima Miroku, telling him in the process that they need to stop tracing their older sister's footsteps. It hasn't happened yet from where she's being pulled from, but she's definitely gone through enough at her point to do so a second time.

Her relationship with her older brother is Special with a capital s. For someone who tries to be so independent, she probably depends on Hiro'omi a lot more often than she should, counting on him whenever things go wrong from both ends of the spectrum — that is, no matter how petty or serious the situation may be. There's no forgetting to mention that he has a huge little sister complex as well, to which she reacts in strong ways: calling him perverted, gross, disgusting, creepy, and telling him to go die (do you see a pattern here) on multiple occasions. They're shown to get into a lot of trivial fights, usually one-sided on her end (his vagueness is frustrating) but much like with her sister, she still looks up to him and trusts him a great deal, probably even more than Izumi at this point. She respects him as a fellow Spirit World Warrior, believes in his strength when the goings get bad, and shows a lot of concern when he gets himself in danger, which is often for her sake and her fault to begin with. She can be pretty naive, displayed when she agrees to let Miroku drive her home thinking she could extract information from him. His real motives were to use her and when he later attempts to attack her, it's her stalking brother that ends up swooping in to the rescue. From the final arc of the series (starting where she's being taken from), their relationship is managing to evolve from Mitsuki simply relying on Hiro'omi to them being able to rely on each other: where they manage to defeat a powerful youmu together and as aforesaid, her giving him the shove he needs.

As if it runs in the Nase family, she's shown to dote on others, such as with Mirai when offering her a portion of her meal and letting her get away with things she wouldn't normally. Her pet youmu Yakiimo is included in this as well, spoiling him so much at one point that there was a period in time where he was too unfit to help her defeat other youmu as he usually does, running a few steps before lying down in exhaustion.

So ultimately, while Mitsuki's personality hasn't changed much at all from start to finish (she speaks as callously as ever, still teases and pokes fun relentlessly), she's done a fair bit of growing up actually cementing herself as a part of the main cast by being less passive, and has in general become a little softer around the edges. There's still a lot left to be desired about her interactions with other people (too brusque, too formal), but it's a work-in-progress now that she no longer has reservations befriending others.

Abilities/Powers:

Being a part of the Nase family, Mitsuki is able to erect barriers that have both defensive and offensive capabilities. They're often used to enclose areas but can also serve as a screen — ordinarily, they act as any normal barrier should (deflection of attacks and projectiles and/or the prevention of things from entering or leaving, it should be noted that certain presences can be blocked if not all of them) but can "collapse" on what they're encasing as well causing what is inside to cease to exist. This takes a lot of power however, and it's not done terribly often — only when the foe is weakened or if it's a last ditch resort (in which the person who created the barrier will go down with them). They also seem to have other functions, such as being able to detect the movement in and out.

Normal people cannot see (or detect) these barriers and depending on its strength, other Spirit World Warriors may not be able to as well. Depending on how it is set up it can appear as if nothing is happening on the inside to outsiders and just display a regular scene.

Let's not forget to mention that the Nase are very particular about calling them "cages" instead of barriers.

As a Spirit World Warrior in general, she's able to detect the presence of youmu (strange supernatural creatures that are found in their world), though only to a certain extent, depending on various factors (how close it is, how powerful it is, et cetera). Whether this extends to supernatural creatures in general will be discussed with the rest of the cast.

Items/Weapons: Shiba Hime gravure issue, box of animal crackers, school bag (contains obsolete writing utensils and a blank book, as well as a change of gym clothes)

Sample Entry:

mmo musebox sample, dear player sample

Sample Entry Two:

All things considered, it could be worse.

It could be a lot worse.

— Either way, Mitsuki takes the situation in stride, head held up high with expression indifferent; it wasn't as if she'd allow herself to do otherwise. While both the surrounding land and people were foreign to her and that the weight on her shoulder that was usually there just wasn't present, she manages to put disconcerting feelings aside to focus on the task at hand. Every so often her hand comes to gently rub at her shoulder and her hands reach to check her phone's screen — but beyond that, she doesn't show any other signs of discomfort.

It's different being truly alone, and she's starting to realise that even before Kuriyama Mirai found herself transferring where she did, Mitsuki never really was.

Hand squeezing the book (that's devoid of words, par the course) extra tightly for a split second, she sooner releases a tired huff before loosening her hold, pushing it back to where it belonged. She'd lost count by now of how many she'd leafed through, knowing only that she'd barely put a dent wherever she'd found herself — an old library, most likely — it was hard to tell through faded furniture and structure that looks as if it's about to crumble on itself any minute, but she persists regardless of the present danger and dusty atmosphere; she grimaces every so often but really, it's her only bet. The Nase family was persistent, and would not allow themselves to be defeated so easily and — she takes the next book off the shelf to go through that.

She had to find at least something after all of this, she had to.