Kousuke and Natsume have been friends since childhood, but as time goes on, the relationship between the two sixth graders seems strained as they keep avoiding each other. One day during the summer vacation, they visit a housing complex that is scheduled to be demolished. Having grown up there, the place holds a lot of memories, but while playing, they suddenly get caught up in a mysterious phenomenon. When they regain consciousness, they see an entire ocean before them as the housing complex has drifted into a mysterious sea with Kousuke, Natsume, and others in it. Will they be able to return to their previous world? A summer farewell journey begins...

Jun Naruse is a chatterbox whose life is colored by fairy tales and happy endings. However, influenced by her deep belief in those tales, she is too naive and trusting, and her words soon shatter her family's bond when she inadvertently reveals her father's affair. Naruse is scarred for life after being blamed for her parent's divorce, and her regrets soon manifest into a fairy egg—a being who seals her mouth from speaking in order to protect everyone's happy ending. Now, even in high school, Naruse's speech remains locked by the fairy egg. Even trying to speak causes her stomach to twist. Though unable to convey her thoughts through words, she is unexpectedly chosen to perform in a musical alongside three other students: Takumi Sakagami, Natsuki Nitou, and Daiki Tasaki. Naruse makes her way to the club room to reject the daunting task, but changes her mind when she overhears Sakagami's beautiful singing. Perhaps the fairy egg "curse" does not apply to singing, and perhaps Sakagami is the fairy tale prince she has been seeking all along. Will Naruse be able to convey the anthem of her heart? [Written by MAL Rewrite]

Long ago, the king of Orvelia, Kyle, defeated the demon king Angmund and brought peace to the world. However, one hundred years later, demons have been sighted in the forests, threatening humanity once more. A scouting expedition is sent to verify the claim but only one member returns. Meanwhile, Riheet, the leader of a dark elf mercenary group, plots to take over Orvelia to exact revenge against the humans who forsook their race a century ago. The knight apprentice Kasel, accompanied by the priestess Frey, sets out to rescue Clause, an old friend who went missing in the tragic mission. However, along the way, Kasel discovers that he is the son of the revered King Kyle and the only one who can wield the Holy Sword Aea—the same sword that slew the demon king. To fulfill this destiny, the young knight must embark on a perilous quest, unseal the sword, and end the fear instilled by demons. As Kasel's journey to bring hope to humanity and Riheet's vow for vengeance intertwine, what fate could possibly await them?

Alternative version of final four episodes of High School DxD BorN.