Kotori Hasutani (蓮谷小鳥, Hasutani Kotori) is a third-year student at Matabi Academy and the Vice President of the Student Council. She is the owner of Musashimaru.
Kotori is a teenage girl of comparatively short height. She has brown eyes and black hair with two puffy pigtails. Despite her short stature, she has notably large breasts, as observed by Tsukasa. She is most often seen wearing her school uniform.
Kotori is kind and compassionate and has strong a belief that problems should be dealt with through talking instead of violence.
As a child, Kotori was close friends with Kaiya Yamamoto. He was shorter and weaker than her at the time, so she always looked out for him. She told him to drink milk and jog every morning and he did so, resulting in his eventual muscular physique.
When Kotor was eleven years old, she received Musashimaru as a gift from her parents. Since then, she always served as her classes' president or vice president and developed a belief that all problems could be solved through discussion. However, two years prior to the start of the series, this belief was tested when she learned her parents were getting divorced despite being assured that they discussed it as much as they could.
At some point during her time at Matabi Academy, Kotori witnessed Kaiya dumping a second-year student that was attracted to him. Kotori later asked him why he dumped her and replied that he was fine with things the way they were.
At the start of the series, Kotori makes her debut appearing before the Matabi Academy students at the first morning assembly of the new school year. After the assembly, she meets up with Tsubame Akifuji and Tsukasa Hinode, informing them that they have been summoned by Shin, the student council president. Once Tsukumoishu attacks the school, Kotori appears before him along with the other student council members. Tsukumoishu then summons a swarm of leaf minions that Kotori and the others must deal with. The leaf minions disappear after Yumi Hayakawa and Kansuke defeat Tsukumoishu.
The day after the battle, Kotori is with the other student council members as they observe that Kaen's seal has been broken.
Two weeks after Tsukumoishu's attack, Kotori meets with Yumi to discuss the events regarding Kaen and what they would wish for if they were to defeat Kaen. Their talk is interrupted, however, when a giant boar demon emerges from the forest. Kotori attempts to talk to and reason with the boar, but it shows it has no intention of listening to her, Kotori and Musashimaru are forced to attack. Musashimaru easily knocks the boar on its back, but when Kotori approaches a giant millstone the boar was carrying, she is caught in a vortex and nearly sucked inside the millstone which the boar says will crush her to death. At the last minute, though, Shin Kamio arrives and slays the boar, freeing Kotori, though she is upset that Shin killed the boar.
The day after her battle with the boar demon, Kotori instructs Tsukasa and Tsubame to fill out a bunch of forms, apparently still upset over her loss.
Later that day, Kotori meets with Kaiya at "The Hill for Confessing Love", as deemed by the girls at Matabi Academy. However, rather than a love confession, Kaiya simply asks her to sew up his tattered uniform. Flustered, Kotori slaps him, but nevertheless agrees to fix his uniform. Kaiya then asks her about her battle with the boar demon and her attitude about the spirit beasts in general. Kotori says that she'd like to talk things out with the spirit beasts, but knows that a 1,000-year-old grudge will be hard to overcome. Kotori asks Kaiya how he feels and he replies that he hasn't thought about it, but knows what he needs to do. Kotori replies that he is acting strange. Kaiya agrees and then leaves.
After Yumi, Tsubame, and Tsukasa battle and defeat the spirit beast Rachi, Kotori arrives at the school infirmary where Tsukasa is recovering. Yumi and Tsubame are also there and they discuss the possibility of other possessed students. They determine that the spirit beasts must be acting discreet so as not to attract attention from the outside world.
Some time after the Rachi incident, Yumi and Kansuke are lured to the spirit beast Daraku. Kotori is notified of this by two of Yumi's friends, which turns out to be a trap set by Sakira, another of the spirit beasts. Unaware of the deception, Kotori takes Musashimaru and goes after Yumi and Kansuke.
As Yumi and Kansuke struggle to fight off Daraku, Kotori and Musashimaru arrive in the forest where they are fighting, but become lost in the fog. They are soon confronted by Daraku's zombie hoard and Musashimaru fights them off. However, the zombies soon dissipate as Shin destroys the lead zombie that was giving them life.
As it begins to rain, Kotori and Musashimaru finally meet up with Yumi and Kansuke. Believing the battle to be over, Kotori instructs Musashimaru to take all the abducted students back to the academy, but Yumi reveals that Daraku has not yet been defeated. Daraku then suddenly appears attacking them with a bolt of lightning. Musashimaru attempts to fight him off, but is electrocuted by Daraku's storm cloud. Kotori falls off Musashimaru, but is caught by Kaiya who arrives just in time. Kotori goes back to Musashimaru and the group concocts a plan to defeat Daraku. Using Kansuke as bait, Musashimaru pulls Daraku out of the water with a fishing line, after which Shin delivers the killing blow. After the battle, Daraku, still alive, utters his final words, claiming that the barrier will be reversed. The group then sees smoke in the distance and heads back towards Matabi Academy.
Kotori departs with Yumi and Kansuke riding atop Musashimaru and emerge from the forest and witness a giant hole in the sky, signifying the reversal of the Futakago Barrier. They then arrive at the academy to witness Tsubame, who has been possessed by Kaen, depart with the other spirit beasts through the Futakago Barrier.
After Kaen leaves through the portal, Shin and Kaiya chase after him and Kotori and others are left behind. Futaba uses her powers to heal Kotori's and the others' wounds and she tells them to rest and get changed and return in an hour if they are wiling to fight. After she has prepared, Kotori goes to Yumi's dormitory and tells her that there is big trouble.
Kotori explains that she tried to get everyone to evacuate the school, but the barrier surrounding the school has trapped everyone within. Kotori and the others are then attacked by a group of spirit beasts that had been summoned by Tsukumoisshu. Kotori and Musashimaru stay behind to fight two of the spirt beasts, while Yumi and Kansuke chase after another beast, while also escorting Yumi's friends to the school gymnasium where all the other students have been gathered.
Kotori and Musashimaru's battle with the spirit beasts eventually takes them back to the school, where it appears Kotori and Futaba will have to stay behind to fight the spirit beasts. However, Shin arrives and declares he will stay behind and fight off the spirit beasts himself, while everyone else goes on ahead. Kotori then departs for the Futakagao Barrier with the others.
Kotori and the others go through the portal, taking them inside the Futakago Barrier, and they find themselves transported to a strange floating island with six floating pillars. The group presses onward towards a palace in the center of the island where they believe Kirihime and Shirayuki are located. On their way, Yumi asks Kotori about her relationship with Kaiya. Kotori reveals that the two were childhood friends and she always had to look out for him. Though concerned about Kaiya, Kotori believes that that he'll be okay.
The group soon discovers a hurt and abandoned Hisui and Kotori takes her in her arms, asking where Kaiya is. They are then approached by Kaiya who is revealed to have been possessed by the sacred spirit beast Kibao all along. Kibao battles them, but they are easily overwhelmed. Kotori begs Kaiya to stop, but it is no use. Kibao then unleashes his true power in a final devastating attack. As the attack bears down on them, Kotori regrets that she and Kaiya never confessed their love for each other. However, Kansuke stands his ground, calling Kibao's bluff, revealing that Kibao never intended to kill them. Hisui explains that Kibao and Kaiya only fought them to stop them from going any further to protect Kotori. Kibao then gives Kaiya control of his body again and Kotori slaps him and tearfully asks why he didn't tell her. Kaiya then explains how Kibao possessed before returning control of his body to the spirit beast. Kibao then explains the history of the spirit beasts and Kirihime. He also explains that he wishes to fight alongside humans, but also wants the spirit beasts to be freed. Therefore, he will attempt to stop Kotori and the others until the spirit beasts are released.
Akitaka Sandou Arc
After hearing Kibao's explanation, Kotori intercedes stating that, while she sympathizes with the spirit beasts, she cannot allow the Futakago Barrier to be opened unless there is a truce. Since Kibao and everyone else agrees that will never happen, Kotori decides to stay behind and fight Kibao with Musashimaru while the others go ahead. Hisui objects, saying that their forces combined couldn't hurt Kibao and she'll be fighting Kaiya. Kotori replies that it she wants to fight him because it is Kaiya. Musashimaru and Kibao begin to fight and the others continue onwards.
Later, after Kaen kills Kirihime and Shirayuki, Kotori and Kibao stop fighting and rejoin the others. Since the spirit beasts have been released, Kibao upholds his agreement to help the humans however he can. However, Kotori and Kibao are intercepted by Hakubi who begins to battle them.
However, their fight is interrupted as the rubble from the island begins to swirl and come together at one point. Kiba leaves Kaiya's body and Kotori and Kaiya return to earth to join the rest of the student council. They go before a large temple that has appeared and witness the rebirth of Sandou, who hid his body among Tsukumoisshu's skull collection. The spirit beasts attempt to destroy Sandou, but he only absorbs their powers, making him stronger. Sandou then explains that six large pillars have been around since before the spark of life itself and are the source of Futakago's power, as well as all magic and spiritual power. He plans to use the pillars to return that power to the world and become the leader of the spirit beasts.
After Sandou finishes speaking, he abducts Yumi, and knocks Kotori and the other student council members away. They soon awaken in a forest with Kibao and find that they cannot use their powers. Nevertheless, they are determined that they must do something to stop Sandou.
Kotori and the others then discover an arrow that was shot by Tsubame that leads them to the magic formation that Sandou is using to conjure his powers. They destroy it, which enable Kansuke to deliver a killing blow to Sandou.
With Sandou defeated, Kotori and the rest of the student council meet up with Yumi and Tsubame. Kaen then appears before them, stating that the spirit beasts have scattered and he will try to keep his existence a secret. The group then realizes they can no longer communicate with their cats. They are disappointed, but know it is for the best.
Three months later, Kotori and the other students of Matabi Academy have relocated to an unused school and readjust to normal life.
Kotori's power is the ability to materialize food, which she gives to her partner Musashimaru, enabling him to grow in size.