13 (debut), 15 (ending)
Ao is the biological son of Renton Thurston and Eureka, technically making him Ao Thurston. He has his father's facial features and brown hair (until he piloted the Nirvash Neo for the first time and it turned turquoise like his mother's) but has his mother's eye and skin color. His mother one day fell from a clear sky into a bay in Iwato Jima, before giving birth to Ao sometime later. After Eureka was handed over to the American Armed Forces ten years ago, as the islanders believe her and Ao's presence angered their local deity the "Sea Colossus" with the appearance of Scub Coral, Ao ended up in the care of his mother's only friend Toshio Fukai. Ao discovers the RA272 Nirvash Mark One after he unintentionally retrieves his mother's bracelet from Gazelle who was smuggling it for the Japanese Army, and then Gazelle gets him to pilot the IFO, both named the Nirvash by Eureka and created by Renton. Ostracized by the villagers and targeted by the armies of several countries, Ao decides to join Team Pied Piper of Generation Bleu, hoping to find her.
It is revealed that Ao has a slightly different genetic makeup than a normal person (due to being a Human-Coralian hybrid) but only that he sees things slightly in the infrared range is known such as being able to see the movements of Trapar. This becomes a setback for him while in space because there is little to no Trapar there. The incidents in episode 11 reveal that Ao belongs to a class of people that can be influenced by trapar. This class consists of people that are born near a Scub Burst, wherein Generation Bleu concluded that their brain structure have been altered by the Scub. The exceptions to this are Ao and Elena, who were not born near a Scub Burst. In episode 12, it is revealed that Ao can apparently see trapar, and calls it the "path of the wind".
Ao is a brave and empathetic boy who is willing to protect his friends and family. He is more upfront than Renton was at his age, according to Eureka. In many ways, he has a combination of both of his parents' personalities; he has Eureka's bravery and Renton's willingness to protect his loved ones. He is kind of shy around girls like Renton was but he is more open with it. He is shown to be reckless, like Renton had been; seen when the Nirvash's arm broke and he used it to smash the Secret. Despite growing up without either of his parents in his life until he was 13, he turned out to be a pretty grateful kid, who was willing to repay them for giving him life and preserving it by saving his mom and making sure she reunited with his dad.
Ao was born as Ao Thurston to Renton and Eureka. In episode 14 and 24, it is revealed that he is actually their second child; their first child, a girl, died 3 months after birth. Before his birth, his parents were trying to use the Gekko to solve the disappearances of Scub Corals. Before completing their mission, the coral vanished, taking his mother (then pregnant with his sister) and the Gekko with it and sending them to the year 2025. Ao met with his mother (from the future) and helped send her back to her time. Upon learning that the high trapar density environment was the cause of their first child's death and made it impossible for a Human-Coralian hybrid to survive, his father decided to send his mother (pregnant with Ao) to the year 2012, where the environment would enable Ao to survive. He was born on the island of Okinawa, and despite being shunned by the villagers for the strange origin of Eureka, he was well-loved by his mother. Three years after his birth, his mother was taken by the United States Government, never to be seen again. He was placed in the custody of his mother's only friend, Toshio Fukai, who adopts the boy as his grandson and he was renamed Ao Fukai. His hair was brown unlike Eureka's aquamarine dyed dark hair, but this doesn't avoid to rouse suspicion from the villagers who shunned his mother. That resentment was later passed on towards Ao, who couldn't understand why he was hated so much for being a "foreigner". It is shown that Ao can and know how to drive an FP despite his short age. Having been ostracized by the villagers, Ao set out to find his mother and learn the origins of his existence.
With his neighbor and friend, Naru, Ao discovers the Nirvash that his mother had piloted before her disappearance, and with the bracelet she left behind, the Nirvash recognizes Ao as its new pilot. In his first fly with the Nirvash, his hair changes to turqoise (similar to his mother's) probably as a result of the contact with the Nirvash. Although inexperienced, Ao quickly becomes a skilled pilot, almost surpassing the skills of his parents when they were his age. Ao joins the Generation Bleu and is assigned to Team Pied Piper, seeing it as an opportunity to find any information on the whereabouts of his mother. Although he quickly becomes disliked and untrustworthy by the government (due to him being Eureka's son), he persists with his goal to reunite with his mother, and eventually becomes one of the best pilots of the crew. When his crew mates find out that his mother is a Coralian, they tease him in play for being the son of an "alien". Although, Ao is deeply affected by this due to how the villagers rejected him and his mother.
In episode 13, he finally reunites with his mother, except he learns that she is from the past, due to that she is still pregnant, and doesn't recognize him. He learns from her that, in her time, she and her husband (and Ao's father), Renton, were trying to solve the disappearance of the Scub Corals by using the Gekko. But in the process, the coral vanished, taking her and the ship with it. He helps her return to her time, but not before asking for her to give birth to a healthy boy. To his shock, she reveals that she is actually carrying a girl. Ao is unable to get any information about his sister and reveals to Toshio that he always believed his father abandoned him and his mother. Toshio, however, reveals that his father is actually fighting for the lives of Ao and his mother. Ao feels a little guilty for hating his father, but is still too confused to understand why his father is not in his life. He continues with his goal to find out more about his mother, and with the help of Elena, Ao learns that the cause of his mother's disappearance is due to her trying to materialize with the Quartz, causing her to become limbo between different worlds, which explains her holographic form.
In the final episodes, Ao discovers that the planet is threatened by the Secrets, which have arise shortly after a Scub Burst. Due to Naru and Eureka's claim that the Secrets are not enemies, Ao is forced to choose between following the governments' order to destroy them with the risk of killing civilians, even though he believes taking lives is wrong. Ao's enemy, Truth, is revealed to be a Secret, and his uncontrollable rage subsequently leads to a rampage on the group. Ao obtains a new weapon, the Quartz Gun to destroy the Secrets, but he learns that his actions changed history, and only he realizes this. Upon realizing that Truth's current form as a Secret can kill people infected by the Scub Corals, Ao decides to fight against Truth, who then destroys himself with the Quartz Gun.
During the final battle against the Secrets, Ao meets his father, Renton, for the first time. Ao witnesses Renton's Nirvash Neo emerging to his side and destroy a large Scub plant in one shot, and the Scub is absorbed by the Quartz Gun. Renton uses the security code on Ao's Nirvash and demands to know where Eureka is, however, he notices that Ao has Coralian eyes and realizes that the boy is his son. The Pied Piper team tell Ao that Eureka has appeared on the Triton, and after she tells Renton that Ao is just like him and has what he wants, Ao realizes that Renton is his father. After getting over the initial surprise, Ao still wanted to punch his father, but is held back by Ivica. Ao learns from his father that the Scub Coral found a way to travel between universes in order to avoid the Limit of Questions, and used the Quartz to achieve this. It is believed that Eureka turned herself into Quartz, and because she wished to be teleported to a different time and place, she was unable to materialize at a particular destination. The only way to change history is to use the Quartz Gun, but Ao says that there is only one shot left. On the island of Okinawa, Ao asks his father what he was doing while Eureka was missing for 10 years, and Renton says that for him she has been gone for a short time. Father and son start to play soccer as Renton goes on to explain that he and Eureka used the Gekko to travel to Ao's world after learning that the Scub Coral had travelled into the world's past in order to evade the Secrets. But the Secrets pursued the scubs through their holes in time, causing the Scub Bursts. Due to this, mankind would become extinct in the future, and eventually, the Secrets considered him and Eureka as enemies and attacked them while she was pregnant with Ao. To save her and their unborn child, he forced her to enter the pillar of light to be teleported to Ao's world, while he stayed behind and killed all the Scub because he didn't want her to kill her own kind. Ao asks Renton why he's trying so hard to destroy the Scub, to which Renton responds that it's his responsibility as an adult; they had once fought to protect the Scub and inadvertently caused the Scub Bursts to happen. Renton quickly leaves and tells Ao that he's going back to the future, taking the Nirvash and Quartz Gun with him. Before Ao can go after him, Toshio pulls him aside to tell him something. Afterwards, Ao still decides to stop his father from destroying the Scub Coral because he still thinks Renton is wrong.
Ao chases after his father, who apologizes to the boy and tells him that he will use the gun to destroy the Scub Coral, and erase them from all the timelines. Ao angrily tells him that there is only one shot left and is worried that his mother will disappear due to her state of limbo between worlds. Renton tells Ao that she is prepared for the outcome, and father and son begin to battle each other with their own Nirvash. Truth, who became an archetype of the Nirvash, speaks with Ao. Renton orders Ao to get out of the Nirvash because it shouldn't have an archetype. Ao fires at his father to steal the Quartz Gun from him, and confesses that Toshio told him about his sister. According to Toshio, Ao's older sister died shortly after she was born because the high trapar density environment caused the human and Coralian cells to reject each other and she turned to stone. Renton and Eureka wanted their second child to be raised in a world with less trapar, and destroyed any Scub Coral that did exist in his world in order to protect him. Ao is happy and touched of the sacrifice his father made in order to keep him alive, but tells him it still isn't right because Naru is infected by Scub, and is worried that she and others infected will disappear, which doesn't right the wrong. He takes the Quartz gun and heads to the pillar of light to save his mother. His comrades from Generation Bleu call out to him, and he begins to say something to Fleur but is cut off as he enters the pillar of light. He travels 10 years into the past, when Eureka disappeared. They happily reunite, and when Renton arrives, Ao tells his mother to go with his father and he will send them home. Eureka refuses to part with him, but decides to leave with Renton after Ao makes it clear to them that he wants to repay them for giving him life and sacrificing so much to protect him. Using the Quartz gun, Ao absorbs all the quartz and fires it at the Secrets in the sky, destroying them and erasing them from all timelines. As he watches his parents return to their time, Ao sees a different Earth, one in balance with Coral and the moon with his parents' names carved into it, much to his embarrassment and amazement.
During the next two years, Ao travels in between worlds in the Nirvash. Truth informs him that he has arrived in the year 2027; however, due to him changing history three times, no one will likely remember him. Ao accepts the possible changes, saying that him being forgotten by everyone is nothing compared to what his mother went through. Using his ref board, Ao bids farewell to Nirvash and truth, promising to meet with them again, before heading towards Earth to resume his life.
Ao's biological mother and the heroine from Eureka Seven. Ao loved his mother so much when he was a toddler and missed her a lot when she left. When he met her past self, he was surprised to see her but was sad when he heard she from the past and was shocked to find out she was pregnant with a girl, leading him to realize that he had an older sister. Although the purpose of him joining the Generation Bleu was to find her, he loved her so much that he was willing to save her from her fate and have her reunited with her husband, and send them back to their world, despite knowing he might never see her again. Ao later told Truth that he did this because his mother had suffered enough hardships, which were coming to a different world to give birth to him alone and fought her own kind to protect him. He also wanted to return the happiness she had been denied with his father for a long time.
Ao's biological father and the hero from Eureka Seven. Ao had always hated Renton when he was a kid because he thought he was a deadbeat father who left him and Eureka. After hearing the truth from Eureka's past self and his guardian telling him that Renton was fighting for them, his hatred towards him lightened, but he still wanted to punch him when they first met. Ao later finds out that Renton, upon learning that high trapar concentrations would make it dangerous for a Human-Coralian hybrid, sent Eureka to a different world in order for Ao to be born and raised in a safe atmosphere, even it meant risking his own life and happiness to ensure Ao lived. He also did this out of guilt for not being able to do the same for Ao's older sister, who died. Saddened by the sacrifices his father made to keep him alive, Ao decided to save Eureka and reunite her with Renton, and sent them to their world and now loves his father. As a child, Ao closely resembled Renton when he was that age.
She is one of Ao's teammates and friends. Initially, Fleur saw Ao as a foolish and reckless IFO pilot, frequently critiquing him for any mistakes he made while on missions and not refer to her so casually by just calling her Fleur. Fleur starts to change her attitude towards Ao after the mission in Faisal Arabia, where they collaborated to help save the people there. During the mission there, Fleur reveals the reason she hates her father, Generation Bleu's President Christophe Blanc. They became friends after this, finding some mutual anger for her father, and she is frequently seen teasing Ao about Naru. She appears to have romantic feelings towards Ao because of the blush on her face and her deep concern for him. In the end she was sad when Ao was sacrificing his existence to save his parents from the fate that they had decided upon. At the end, Fleur was shown to have chased Ao to the Scub burst with the Alleluia's third engine activating. Her fate, however, is left unknown after Ao used the Quartz Gun for the third time; it is possible she may not remember Ao at all.
She is Ao's childhood friend and she is one of two people on the island who don't see Ao as an alien or monster. Although her father despises Ao and blames him for all of the island's misfortune, Naru has a strong bond with Ao, and often tries to keep him in line. Ao cares deeply for her, to the point where his crew mates (namely Fleur and Elena) tease him for being romantically interested her, although both Ao and Naru maintain they are just friends. His concern for her gorws when she is revealed to be a coral carrier, which damages her health. She later join forces with Truth to bring a new era where people can trust the Coral then people would like Ao. However, after she realizes Truth has deceived her and he was killed by the Quartz Gun, Naru is hospitalized. It is unknown what happens to her after Ao shot the Quartz Gun for third time; other than she grew up healthy and may not remember Ao.
- It is revealed by Gazelle that Ao hates his father. This reflects Renton's hate towards his father, Adroc, believing that his father cared more about his research rather than his own family. However, it's revealed by Eureka that Adroc did care for his family and that's what caused Adroc to vanish which causes Renton to forgive his father. Now, Ao bears a similar hatred because he believes that Renton left him and Eureka when Eureka arrived at Iwato Island. But then the past Eureka and his guardian reveal that his father always loved Eureka and that he is fighting for her and Ao. This allows Ao to let go of his hatred towards his father and now kind of loves him. It is also revealed that Renton sent Eureka to Ao's world because he wished for Eureka to bare a child that would not be turned into stone due to the atmosphere.
- Despite not meeting him until the final episode, it is shown that Ao and his father have a lot in common in personality and interests. They care deeply for others, they are against violence but are willing to fight in order to protect their loved ones, they are shy around girls, and they like soccer and later lifting. Renton even gave Ao his old ref board as a farewell present.
- Because Ao didn't know his father's name until episode 13, it seems that Eureka never told Ao about Renton and the reason for his absence in Ao's life.
- Although his legal name is "Ao Fukai" in the world the series takes place, his birth name is "Ao Thurston" due to his great-grandfather formally marrying Renton and Eureka in "Wish Upon a Star" of Eureka Seven.
- Although Ao lives with his adopted grandfather, he revealed that he can make by on his own because he does odd (and illegal) jobs, possibly to lesson the burden on his grandfather of raising a child that is not biologically related to him and is the object of resentment and hostility from the villagers.
- While aboard the Gekko in episode 13, Ao wore the track suit his father wore in "Absolute Defeat" of Eureka Seven.
- Ao was born in the year 2012, the same year both the anime and manga started. His birthday is June 27, 2012.
- The name Ao means "deep blue" in Japanese.