20 November, 2012
15 October, 2013
The Door Into Summer (夏への扉 Natsu e no Tobira) is the twenty-fourth and final episode of the anime series Eureka Seven: AO. It was part of the hour-long ending of the anime series shown on November 2012 together with the previous episode, The Final Frontier.
Ao, shocked that he is seeing his father, Renton, for the first time in his life, attempts to punch him, but is held back by Ivica, who asks Renton about Eureka's situation. Renton explains that the Scub Coral, aiming to avoid the Limit of Questions, sought a way to travel between universes and used Quartz to achieve this. Renton speculates that Eureka must have turned herself into Quartz when she attempted to dispose the collection of Quartz, and she wished to only be transported to a different time and place, which caused her to be unable to materialize at a particular destination. Ivica and Rebekah tell him about the Quartz Gun and it's ability to alter the course of history when it's used. Ao, however, tells him that there is only enough charge for one shot and its what he's been looking for, just as Eureka said.
On the island of Okinawa, Renton thanks Toshio for taking care of Eureka and Ao. Ao asks his father what he's been doing while his mother was missing for 10 years. Renton says that to him, she has been gone for a short time, and asks Ao if he likes soccer. Meanwhile, everyone from Generation Blau, mainly Hannah, is questioning whether or not Renton is another threat to them. Ivica assures everyone that Renton is Eureka's husband and Ao's father, therefore he is not a threat.
Back at the Fukai residence, Renton and Ao play soccer. Renton explains that Eureka used the Gekko to travel to Ao's world after learning that the Scub Coral had travelled deep into the world's past. In the year 12006, following the events from the end of Eureka Seven, the Scub Coral arrived in the future of Ao's world but their appearance triggered the appearance of the Secrets, which were produced naturally to prevent the Scub Corals' invasion. The Scub Coral began traveling to different timelines to escape from the Secrets, but Secrets pursued the Scub Coral through their holes in time, causing the Scub Bursts. In the future of Ao's world, mankind would be extinct because of this. Eventually, the Secrets considered Renton and Eureka as enemies as well (possibly due to Eureka being a Coralian). While pregnant with Ao, they arrived in the future of Ao's world in preparation for his birth, but they were attacked, and in order to save Eureka and the baby, Renton forced her to enter the pillar of light to be transported to another time with less trapar, telling her that he would stay and kill all the Secrets and he didn't want her to kill her own kind, the Scubs. Renton tells Ao that Eureka gave birth to him soon afterwards and did everything she could to keep him safe. Calling him "Dad" for the first time, Ao asks Renton why he's trying so hard to destroy the Scub Coral, to which Renton replies that its his responsibility as an adult; he and Eureka had fought to protect the Scub and unwillingly caused the Scub Bursts to happen, and therefore, he needs to correct their mistake. After kicking the ball hard at Ao, Renton leaves, telling Ao that he's going back to the future, entering the Nirvash and taking the Quartz Gun with him. Ao tries to chase after his father before Toshio pulls him aside to tell him something as Renton flies off with the Quartz Gun. Afterwards, Ao still decides to go because he still thinks Renton is wrong about destroying the Scub.
Using the Nirvash Neo, Ao catches up with his father, who is impressed by Ao's flying skills. Renton apologizes to Ao, who tells him not to. Renton says he will use the Quartz gun to destroy the first Scub Coral in the world, erasing it from all the timelines and returning everything to normal. Ao angrily tells him that there is only one shot left and is worried of what will happen to his mother due to her being in limbo between worlds. Renton says that Eureka is prepared for the outcome, and father and son begin to battle in each of their Nirvash over the Quartz Gun. Truth speaks to Ao, having become the archetype of the Nirvash Neo. Renton angrily attacks the Nirvash Neo, demanding to know why it has an archetype and tells Ao to get out of the Nirvash. Ao fires back at his father and the Quartz Gun is dropped, which begins to fly high into the sky and they pursue it. Renton tells Ao to not interfere. Ao says that Toshio told him about his sister, shocking Renton. In the earlier conversation, Toshio revealed to Ao that his sister, Amber, turned to stone and died when she was 3 months old; in a high trapar density environment, the human and Coralian cells in the baby rejected each other. When Eureka became pregnant with Ao, Renton decided their son had to be raised in a world with less trapar, and chose the world Ao lives in now, which Eureka discovered by accident, so that he would survive. They tried to destroy any Scub Coral that did exist in Ao's world in order to protect him. As Renton cries over the memory of him and Eureka burying their daughter, Ao cries and thanks his father for sacrificing so much to keep him alive but tells him that it isn't right because Naru is infected by the Scub Coral and wonders what will happen to those infected if the Scub Coral s destroyed. Renton says that if they've merged with the Scub Coral, they might disappear. Ao angrily replies that erasing something that's wrong doesn't make it right, and every young life is still a life. Renton says that Ao will turn to stone if the Scub Coral continues to exist in this world, but Ao says that he grew in this world and he wants to protect it. He flies ahead, grabbing the Quartz Gun and heading to the pillar of light, planning to save his mother. Fleur, having heard everything from the Triton, tearfully begs Ao not to go and asks if he was lying when he said they were like a family. The communication is cut off before Ao can reply back. Ao travels 10 years into the past, when Eureka disappeared with the Quartz. He arrives just before she was supposed to vanish, and she happily embraces him. Ao asks her how she knows its him because he would be 2 years old in that point in time. She says that she remembered when he rescued her the first time she arrived in his world, and when she was returning to her world, the degraded Nirvash Neo, with Ao piloting it, told her he is her son, hence how Renton knew Ao's name. She asks why he didn't tell her sooner, and Ao says she wouldn't have believed him and she was pregnant with his sister back then. Renton arrives, and Ao tells Eureka to go with Renton, as he will send them back to their time. Eureka refuses to leave Ao, and Ao says he knows it was hard for her to kill her own kind but she and Renton did so in order to protect him. She says that's not entirely true because someone once told her that she was being selfish for falling in love with Renton and having children, and therefore they have to take responsibility for everything that has happened. Ao tells his parents that they have had to sacrifice themselves for his sake and he believes he was born to free them from their curse of making sacrifices. Eureka cries, and Renton comforts her as he starts to cry, too. As they part ways, Renton gives Ao his old ref board and says the sacrifices he made to protect him were worth it, calling Ao "son". Ao then absorbs all the Quartz with the Quartz Gun. With his parents in the Nirvash close by, Ao vows to save the future they chose, and fires the Quartz at the Secrets, destroying them and erasing them from all timelines. Ao is briefly knocked unconscious, but when he comes to, he sees his parents' Nirvash and a different Earth; one in balance with Coral and the moon with his parents' names carved into it. Ao is embarrassed and amazed of how much his parents love each other before going unconscious again and disappearing.
Two years later, Ao (with long hair) is revealed to have been traveling in different timelines before arriving in the year 2027. Truth tells him that because he changed history three times, no one will likely remember him and it will be difficult for Ao to live a normal life if he is forgotten, and he had said goodbye to his parents forever when he returned them to their world. Ao, however, says its okay because his problem is nothing compared to what his mother went through in order to raise and protect him. Using his father's old ref board, Ao departs from the Nirvash and bids farewell to Truth, promising that they will meet again someday as he watches them disappear to continue wonder through time. He then travels back to Earth's surface to resume his life.
- In a twist of events, Renton and Eureka are trying to destroy the Scub Coral, in contrast to how they fought with their lives to protect it in Eureka Seven.
- It is revealed that the Scub Coral arrived in Ao's world in the year 12006 after the events in the final episode of Eureka Seven, but the Secrets were created in order to destroy them because they viewed the Scub Coral as threat. As a result, the Scub Coral traveled to different times in Ao's world before arriving in the present.
- Renton says that the reason he is trying to destroy the Scub Coral is because his and Eureka's protection for it unintentionally caused the Scub Bursts to occur.
- Ao finds out about the real reason why his father is trying to destroy the Scub Coral; to protect Ao from turning to stone when the trapar concentrations become high.
- Ao finds out that his older sister had died when she was 3 months old.
- In a stunning twist of events, the atmosphere in Renton and Eureka's world is inhabitable for a Human-Coralian hybrid.
- Renton and Eureka's daughter, Amber, died at 3 months of age when the high level of trapar caused the Human and Coralian cells in her to reject each other and her body turned to stone.
- Ao believes his father is making a mistake by wanting to erase the Scub Coral's existence and decides to destroy the Secrets instead.
- Ao is able to save his mother and reunite her with his father, and express his forgiveness and affection towards his father.
- Renton and Eureka chose to give up their relationship, happiness, and almost their lives in order to keep their son alive because the death of their daughter is what motivated them to do whatever was necessary to save their son, including destroying the Scub Coral.
- Ao sacrifices his existence in order to save his parents and return them to their world, resulting in him wandering through time before arriving in 2027.
- The episode title is derived from the song Natsu e no Tobira (The Door Into Summer) (夏への扉 (THE DOOR INTO SUMMER)) in the album Ride on Time by Tatsuro Yamashita. The song's title in turn is named after the novel The Door into Summer by Robert A. Heinlein.
- In the final episode of Eureka Seven, Nirvash had told Renton and Eureka to bring forth a new evolution (have Human-Coralian children) in order to bring the humans and Scub Coral together as one. In contrast, however, the trapar from the Scub Coral makes it too dangerous for a hybrid child, resulting in the death of their first child and forcing them to send their second child to another universe in order to save his life.
- If Renton had used the Quartz Gun to erase the Scub Coral, not only would Eureka be erased but Ao would be too because he is Eureka's child and is a descendent of the Scub Coral. Renton may not have fully understood the consequences of that act or else he would have not done anything to erase the existences of his wife and son
- While Eureka Seven got a happy ending with Renton and Eureka able to be together and save the planet, Eureka Seven: AO had a sad ending with them losing a daughter and giving up a son to keep him alive, and sacrificing everything they achieved for their son's sake.
- While Ao was wandering through time at the end of AO, it is revealed this is when he pulled Eureka back to her world during Starfire (Another Truth); however, he had just learned that Amber will die if she is born in their parents' world. So, he inadvertently allowed his own sister to die.
- The person Eureka described as calling her selfish for falling in love with Renton and having children is never specifically stated. The choices can possibly be Holland, Ray, and Hannah.