Yui has a dream where she sees Apollon speaking to a woman and promising that his love will never change. The woman replies that it is impossible because a god and a mortal cannot live together. As a proof of his promise, Apollon gifts her with the ability to see the future. Yui wakes up and wonders who the woman was.
Apollon falls asleep during class and Thoth wakes him up, reprimanding him for falling asleep in class despite being the student council president. After Apollon apologizes, Thoth announces to the class that they will be having midterm exams in three days. Yui is surprised, saying she thought this academy didn’t have exams. Takeru asks Apollon if he’s able to predict the contents of the exam but Apollon replies that he can’t. The gods decide to study together and Tsukito brings out his notes, but says that he does not understand any of the content. Apollon falls asleep again and Hades wakes him up. He then goes with Yui to the school store to get some snacks.
On the way back Yui asks Apollon if he is okay. However, when Yui mentions how she is happy they have friends to study together with, Apollon stops and says that he must never be happy because he committed an unforgivable crime. Yui is concerned by what he said but Apollon tells her he was kidding and to forget about it. Yui then has a vision of the woman from the dream opening the box containing Apollon’s gift. The woman cries after seeing the future. Upon realizing Yui was no longer with him, Apollon ran back to find her. He hugs her, saying he was scared and thought she was gone. Apollon asks Yui to stay with him forever and not to leave him alone, refusing to let go of Yui after she asked him to. Takeru, Loki and Balder appear at this time and separate the two. Yui recalls that this was like what happened at the seaside school.
In the Greek gods’ dorm, Dionysus comments that Apollon isn’t acting normal and Hades says they should keep an eye on him for a while. The other gods also show some concern over how Apollon had acted. Yui wonders if she should talk to Thoth about it but has another dream. Apollon runs to a river, calling out the woman’s name, Cassandra. He cries after he finds Cassandra’s body floating in the river. Yui wakes up and wonders what is happening. She runs to the balcony and sees Apollon walking off on his own.
She follows him to the riverside and finds him standing before Cassandra’s ghost. Apollon walks into the river, apologizing to Cassandra and saying it’s his fault. Apollon faints after Yui hugs him from behind and Cassandra’s ghost disappear. Dionysus and Hades arrive and Apollon is brought to his room. Dionysus tells Yui that Cassandra had lost all hope for the future and Apollon cried for days after her death. However, Hades comments that despite her death, she never came to the underworld. Due to her attachments to this world, she still wanders this world as a ghost. He tells Yui that sometimes, the dead bear grudges against the living and cause them harm. It is likely Cassandra resents Apollon. Hades warns Yui to be careful since Cassandra may be trying to harm her too.
Apollon wakes up and breaks down, exclaiming that he had killed Cassandra, causing his shackle to turn black. Yui runs to finds Zeus, who tells her Apollon’s shackle glows black because his heart is covered by a great shadow. When he lost Cassandra, Apollon blamed himself and became trapped by the thought that he must never find happiness. That is why Zeus had called him to this garden. If nothing is done, Apollon’s heart will be confined within darkness and will rot. Yui begs Zeus to save Apollon but Zeus replied that he would have if he could. Thoth stops her as she is leaving, asking her what she intends to do. Yui says that she does not know, but she must do something. As she runs off, Thoth comments to himself that humans are such fools.
Yui meets the ghost of Cassandra and asks her to please set Apollon free because he’s very badly hurt and asks her not to hate him anymore. Cassandra tells Yui her words are unable to reach Apollon and the harder she tried the more Apollon is hurt. She, too, wants to save Apollon and asks Yui to lend her strength. Apollon leaves the room, ignoring Dionysus and Hades when they chased after him. He stops when he sees Yui, now possessed by Cassandra’s ghost.
Cassandra tells Apollon that he will live forever and she will die alone. She took her own life because she couldn’t bear this future. But later, she understood that even if they were both human, death would eventually part them. That’s why people treasure their limited time together all the more. However she was a fool not to realize that. Apollon replies that he’s the one who’s the fool, giving her divine power because he wanted her heart. Cassandra tells him not to blame himself and she is now happy with the memories of the time they spent together, and asks him to find his own happiness. She holds him and comforts him as he cries. After thanking Apollon and saying goodbye, Cassandra leaves Yui’s body and thanks Yui before disappearing.
Hades comments sometimes, the dead bear grudges against the living and cause them harm, but sometimes, the love the living and watch over them. With this, Apollon’s shackle returns to normal and breaks. The next day, the gods are all amazed at Apollon’s shackle being gone and enjoy a happy moment before realizing that they had all forgotten about their midterms.