Futaba Aoki (青木二葉, Aoki Futaba) is a third-year student at Matabi Academy and the Health Committee Chairwoman of the Studen Council. She is the owner of Gekko.
Futaba is a tall teenage girl with purple eyes and long black hair that she usually wears in a ponytail. She is most often seen wearing her school uniform.
Futaba has a stoic and reserved personality, preferring to keep to herself.
Prior to the start of the series, Futaba's father was revealed to be a criminal and was apparently stabbed to death. Though he left behind an inheritance, her mother ran off with most of the money. These events earned her the scorn of her classmates who believed she was probably the same as her father. This led to Futaba having a great disdain for people and a fear of betrayal. At some point, she discovered Gekko who was sick and dying and nursed him back to health.
At the start of the series, Futaba makes her debut appearing before the first morning assembly along with the rest of the student council. Once Tsukumoisshu attacks the school, she appears before him alongside the rest of the student council. Tsukumoisshu then summons a swarm of leaf minions that Futaba and the others must deal with. The leaf minions disappear after Yumi and Kansuke defeat Tsukumoisshu.
The day after the battle, Futaba is with the other student council members as they observe that Kaen's seal has been broken.
Two weeks after Tsukumoisshu's attack, Futaba attends another meeting with the student council to discuss the apparent inactivity of the spirit beasts, despite the breaking of Kaen's seal.
After Yumi, Tsubame, and Tsukasa battle and defeat the spirit beast Rachi, Futaba performs medical treatment on Tsukasa to help him heal from an injury he sustained during the fight.
Some time after the Rachi incident, Futaba meets with Shin and their companion cats to discuss the spirit beasts and their infiltration of the school. Shin decides that they will find out the mystery of the school and the center of the Futakago Barrier.
Later that night, Yumi and Kansuke are lured to the spirit beast Daraku and Shin, Kotori, and Kaiya go to save them. They manage to defeat Daraku, which Gekko (having attached his shadows to the cats) reports to Futaba. Futaba asks him to check on Tsubame and Sakura, but they run into trouble as Tsubame sends Sakura away. Kaen then takes over Tsubame's body, which goes unseen by Sakura and, therefore, Futaba and Gekko. Concerned, Futaba and Gekko head towards the building where Tsubame was researching Akitaka Sandou's notes and finds that it has burst into flames.
Futaba then sees the Kaen-possessed Tsubame emerge from the burning building, and Shin and Kaiya arrive on the scene. She attempts to warn them that Tsubame has been possessed, but Kaen attacks them. Fortunately, Kaiya is able to shield them in time. Kaen then taunts them by reciting personal information about them, which Futaba infers he is obtaining from Tsubame's memories, and then shows them that the Futakago Barrier has reactivated. Kaen declares his intent to go through the barrier and kill Kirihime and Shirayuki, but Futaba and the others try to stop him. Futaba uses her light and shadow powers to hold Kaen down, giving Shin a chance to strike. However, Hakubi intervenes and Kaen easily fights Futaba and Gekko. Kaen then gathers the other spirit beasts and leaves through the barrier.
After Kaen leaves through the portal, Futaba tries to dissuade Shin from chasing after him, claiming most of them are too injured and tired from fighting Daraku. However, Shin says that they cannot allow the barrier to be destroyed and goes on ahead with Kaiya. Frustrated, Futaba sends a Moonlight Butterfly after them, hoping it will heal them in time. She then uses her Moonlight Butterflies to heal everyone else. Assuming command, Futaba tells everyone to clean up and get changed and meet back in an hour. She also tells them that anyone of them could die, so they should only come if they truly wish to fight. Suddenly, Tsukasa and Raimu arrive on the scene and Futaba asks them to do something for her.
As the appointed time draws closer, Futaba observes that the entrance to the barrier has gotten smaller. A spirit beast then attacks the school and attempts to kill the students that have gathered in the gymnasium. However, uses her powers to stop the attack and sap the spirit beast's strength. Futaba then orders Yumi, Tsukasa, and their cats to go ahead through the Futakago Barrier, stating that she and Kotori will stay behind to fight the spirit beasts. However, Shin arrives and declares that all of them will go up and he will stay behind and fight off the spirit beasts himself. Futaba accepts and departs for the Futakagao Barrier with the others.
Futaba 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. Futaba identifies a palace and directs everyone to head for it, believing Kirihime and Shirayuki will be there. On their way, they find a hurt and abandoned Hisui and then are approached Kaiya who is revealed to have been possessed by the sacred spirit beast Kibao all along. Kibao battles them, and injures Tsukasa. Futaba then uses her Moonlight Butterflies to heal him while Kansuke and Musashimaru battle Kibao. However, they prove to be no match for him. Gekko attempts to restrain Kibao, but he breaks free by jumping into the air. Kibao then unleashes his true power in a final devastating attack. However, Kansuke stands his ground, calling his 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. Kaiya explains how he became possessed by Kibao, and Kibao explains the history of the spirit beasts and Kirihime. He also explains that he wishes to fight alongside humans, but also wants the spirit beast to be freed. Therefore, he will attempt to stop Yumi and the others until the spirit beasts are released.
Akitaka Sandou Arc
After hearing Kibao's explanation, Kotori elects to stay behind and fight Kibao while Futaba and the others continue onwards. On their way, Futaba declares her admiration for Kotori in that she was able to get a concession out of Kibao and intends to not let her efforts go to waste. The group continue towards the palace, but are met by Sakira, another of the five sacred spirit beasts. Before a fight between them can break out, the island starts to shake and the landscape breaks apart, sending them all plummeting downwards.
As they fall, Futaba and the others experience a vision of Kirihime who shows them a meeting between Kaen and a man name Akitaka Sandou and explains that Sandou has become obsessed with reuniting with her. Once the vision is over, Futaba and the others once again find themselves falling through the air. Yumi uses her yarn to create a parachute and series of hammocks to catch everyone, including Sakira since she is possessing a student's body. Sakira explains that the falling rubble is about to fall on their school and the gate has been opened, meaning all the spirit beasts have been released. Futaba and the others, realizing that they all experienced the same vision, discuss what to do. Futaba realizes they must stop Akitaka Sandou, but first they must do something to save the students beneath them. Suddenly, Kotori and Kibao arrive, the latter having kept his promise to help the humans as soon as the spirit beasts were released. However, the two are intercepted by Hakubi who starts to battle them. Before Futaba and the others can act, they are caught a hypnotic spell by Sakira that renders them immobile and unconscious.
While under the hypnosis, Futaba and Gekko are swallowed whole by Sakira's brother. Inside the snake's stomach, Futaba's mind becomes trapped in an illusionary world created by Sakira. Futaba sees a vision of Gekko who demeans her and shows her her greatest fear; the fear of being betrayed. Sakira wraps around Futaba and prepares to devour her soul, but is stopped by Tsukasa and Raimu who managed to use their Dream Box ability since hypnosis does not work on Raimu. The two defeat Sakira and free Futaba and Gekko from the snake's stomach. Futaba awakens, covered in digestive fluids, but unharmed. As the others awaken, Futaba questions how much time has passed, and Raimu explains that, thanks to the Dream Box ability, almost no time has passed. Futaba and the others then see that the rubble is actually swirling and coming together at one point. They arrive back on earth and reunite with the rest of the student council just in time to see 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 Futaba 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.
Futaba 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, Futaba 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, Futaba and the other students of Matabi Academy have relocated to an unused school and readjust to normal life.
Futaba can manipulate Gekko's shadow to do such things as create drones to spy on others and extend Gekko's shadow which can then act as a portal. She can also conjure "Moonlight Butterflies" that can heal people's wounds. She can also create humanoid light and shadow "avatars". The shadow avatar can sap its enemies strength and the light avatar can heal severe wounds.