Mitsuki Nase (名瀬 美月 Nase Mitsuki) is one of the main characters of the Kyoukai no Kanata series. She is a Spirit World Warrior who hails from the prestigious Nase family, the president of the school's Literary Club  and the youngest sister of Hiroomi Nase.
Mitsuki is a young girl of average height with a kind of curvy but slim figure, fair skin, dark ruby red eyes that sometimes look brown and black hair; a physical trait her family shares. Her lengthy hair remains straight, and styled down her back, with several loose fringes hanging by her forehead, excluding the time she's worn it in a side-ponytail during the festival. She chooses to keep her bangs regardless of how she styles her hair.
Her signature look includes her eating some sort of lolipop or popsicle.
Mitsuki is casually seen in her school attire which consists of a sailor-type, Yale-blue top with white and blue cuffs and six buttons (three on either side), along with a long white and blue striped collar accompanied by a red ribbon. She bears a light blue pleated skirt with a white line trailing along the pleats and calf-length, black socks with white and black shoes with black laces.
Mitsuki is known for her frank way of speaking and acting to the point of looking like she has a sadistic personality. This cold demeanor of hers was influenced by Izumi Nase , who forged the thought that which Spirit Warriors are to focus only upon their duties. Under this monotone posture, she has shown to display other emotions such as anger, sadness or happiness. As president of the Literary Club, she spends much of her time venturing the outskirts of the Literary Club beside Akihito Kanbara (Mitsuki's friend). Her teasing Akihito is one of her comedic properties. Mitsuki also tends to favor sweets and ice cream.
At a young age, she holds a different mentality towards youmu, considering some of them as capable of interacting with humans without any hostility.
As a child, Mitsuki was taught by Izumi Nase to only rely on herself. She also spends most of her life inside the confines of the Nase Residence, preventing herself from making any friends. As a result, she develops a detached disposition towards other people, and only talks with other members of the Literary Club, namely Akihito Kanbara and Hiroomi Nase.
The Half-Youmu and the Hollow Shadow
Mitsuki has been an acquaintance of Akihito's two years prior, by the start of the story. Due to the orders of the Nase family, Mitsuki joins Hiroomi Nase (Mitsuki's older brother) in watching over the half-youmu and make up the small Literary Club so they can meet frequently. After the fateful encounter with the Spirit World Warrior named Mirai Kuriyama, Mitsuki advises Akihito to refrain from meeting up with Mirai. Whether or this was out of concern that Mirai was another Spirit warrior after Akihito or that she might of known about Nase's involvement with Mirai is uncertain. As expected by Mitsuki, Akihito did not follow her request and instead, helps Mirai in slaying her first youmu.
Despite Akihito's actions concerning Mirai, Mitsuki remains her usual self towards him. In a visit to the Shindou Photo Studio, she overhears the message of Yayoi Kanbara (Akihito Kanbara's mother), who is a famous Spirit World Warrior herself, regarding the powerful youmu called the Hollow Shadow. After receiving the message, Mitsuki shows signs of warming up to Mirai, showing no qualms over Mirai joining the Literary Club and helping Mirai in capturing a youmu for additional income, although Mirai remains cautious of Mitsuki's actions.
Later on, Mitsuki slowly becomes suspicious of Mirai and warns Akihito that Mirai may be on a hot pursuit of the Hollow Shadow and is planning to kill it singlehandedly despite the risks. True enough, Mirai stood in the path of the Hollow Shadow and prepares to fight alone, only to be interrupted by a friend-turned-enemy named Sakura Inami, the younger sister of Yui Inami who was killed by the Hollow Shadow several years ago. Mitsuki decides to retreat, leaving the fight to more experienced fighters as the fight triggers Akihito's youmu side to awaken. Akihito's rampage was eventually stopped by Mirai and her blood that can destroy any youmu at contact.
Akihito Kanbara and Mirai Kuriyama survive the ordeal and Mirai was later welcomed into the Literary Club, although Mirai still had to face the consequences of disobeying orders from the Nase family by surrendering her license to Izumi Nase, the current representative of the Nase family. Without a source of income, Mitsuki offers a helping hand by referring her to the youmu owner of the Shindou Photo Studio named Ayaka Shindō for a part-time job as a photography model. Later, after some hesitation, Mitsuki goes to the nearby Lantern Festival for the first time with Mirai.
Mirai manages to get back her license as a Spirit World Warrior after a month of suspension. However, Mitsuki discovers that the Calm is approaching Nagatsuki City, affecting all of the youmu in the area, including Akihito, Ayaka and Ai Shindō (Ayaka's companion). She also learns from the Spirit World Warrior Miroku Fujima that a powerful youmu called Beyond the Boundary is responsible for the Calm and there are links between the youmu, the Nase family and Akihito. Hiroomi, who quickly snatches Mitsuki from Miroku, warns Mitsuki of the possible subterfuge within Miroku's words.
Mitsuki later joins her brother in taking down the weakened youmu in the area and rejoins with Izumi and Mirai, who is in the middle of pursuing Akihito, whose youmu side has taken over for the meantime. Izumi suggests that killing Akihito is the only way to stop him, something that the younger Nases protest against. Despite her memories with Akihito, Mirai chose to save Akihito's life by sacrificing herself in the process.
Beyond the Boundary
Months after Mirai Kuriyama's sacrifice, Akihito Kanbara fully recovers, but soon faces the reality of Mirai's fate. Meanwhile, Mitsuki and Hiroomi Nase slowly feel their powers waning for some reason. Later, Miroku Fujima reappears and uses the weapon that Sakura Inami discarded after reconciling with Mirai to empower the weakened Beyond the Boundary, which has been draining the energy from the surrounding area.
Mitsuki joins the others in knowing more about Beyond the Boundary, particularly the fact that Mirai is still alive and can still be saved. As Akihito decides to help Mirai from inside Beyond the Boundary, Mitsuki joins Izumi, Hiroomi and the others in slaying the youmu that are dragged out by Beyond the Boundary. In a final confrontation, Sakura, Mitsuki, Hiroomi and Izumi face Miroku, but were shocked when Miroku exposes Izumi's nature as a Spirit World Warrior having a youmu inside of her. Humiliated by the reveal, Izumi flees to parts unknown, leaving the clan to Hiroomi and Mitsuki.
After the defeat of Beyond the Boundary, Mitsuki, like everyone else, returns to their daily life and eventually reunites with Mirai, who shows up with Akihito after disappearing inside Beyond the Boundary for some time.
Akihito and Mitsuki always spend their time inside the Literary Club room, exchanging humorous banter with each other, with Mitsuki acting as the tsukkomi . She is typically seen accompanying Akihito due to her task of safeguarding and monitoring him. However she does care for Akihito as friend and shows concern for his well being, when he is hurt or injured even to the point of coming to tears. Frequently in the series, Mitsuki gives Akihito rational advice for various problems.
Despite being warned about Mirai's identity by her family, Mitsuki seems neutral towards her, and somewhat cautious towards Mirai at first. However, Mitsuki soon develops a special bond with her, as they spent time together. In the film Mirai Hen, she reprimands Akihito for keeping Mirai's past secret from her. In the film ending, she runs towards Mirai, hugging her with tears in her eyes.
Hiroomi is Mitsuki's older brother whom they both have the mutual tendency to tease Akihito. Hiroomi and Mitsuki often bicker, but always reconcile quickly. She often seems to be disgusted by his actions. Mostly from the antics of Hiroomi's sister complex, yet is quick to forgive him. They share a strong bond otherwise, with Hiroomi acting as a mature protector when he needs to, and Mitsuki showing him gratitude in return.
Glaciate Barriers 
Like her sibling, Mitsuki has the ability to create special barriers called Glaciate Barriers that can be used defensively and offensively against Youmus. She rarely uses her abilities for offense and relies more on Yakiimo to attack. Despite her capabilities she is not as skilled as her siblings who often times come to her aid in combat.
- The name Mitsuki means "beautiful" (美) (mi) and "moon" (月) (tsuki).
- Mitsuki's surname Nase means "name, noted, distinguished, reputation" (名) (na) and "swift current, rapids" (瀬) (se).
- Nase may be aptly interpreted as "renowned position", considering that the Nase family is a prestigious family among Spirit World Warriors.
- Mitsuki's youmu's name, Yakiimo, literally means "Baked Sweet Potato".
|Main Characters||Akihito Kanbara • Hiroomi Nase • Mirai Kuriyama • Mitsuki Nase|
|Spirit World Warriors||Ayaka Shindou • Izumi Nase • Miroku Fujima • Shizuku Ninomiya • Yayoi Kanbara|
|Youmu||Ai Shindou • Ayaka Shindou|
|Others||Sakura Inami • Yui Inami|