Among the royal court, there is an individual feared as much as revered: the Raven Consort Ryuu Jusetsu. Residing in her jet-black palace and isolated from the emperor, she is the subject of countless rumors. Claimed to possess mystic abilities, she is said to take on any request—from finding lost items to inflicting curses. While some call her an immortal sage, others believe her to be a terrifying revenant. But such comments fail to faze Jusetsu, who prefers to spend her days in quiet solitude. That is, until the emperor, Ka Koushun, barges into her court and asks for her assistance with a mysterious case. The young emperor's request requires Jusetsu to step out of her palace for the first time. Despite Ka Koushun's frequent visits annoying her to no end, she cannot bring herself to turn him away. Her predecessor's teachings echo in her ears: the Raven Consort is destined to remain forever alone and never desire anything. Yet Jusetsu finds herself making the first of several bonds when she asks Jiujiu, an innocently inquisitive court girl, to be her sole attendant. Together, they begin fulfilling requests from the people of the palace. However, unknown perils lurk in the outside world, and drawing attention to herself may bring Jusetsu face-to-face with a past that is better left undisturbed.

Tensions are running high among the clans as the Green King begins making moves that threaten to drive the world into pandemonium. Following the death of the Gold King, the safety of the Dresden Slate, the source of power of the Kings, is under threat. Nagare Hisui, the sly and mysterious leader of the Green Clan Jungle, is determined to procure the powerful Slate by any means possible. Standing directly in his way is Sceptre 4, the Blue Clan, headed by their unyielding King, Reisi Munakata. However, the grim sight of his crumbling Sword of Damocles leaves the stability of his clan and all of Japan in jeopardy. Meanwhile, still recovering from their tragic losses, Anna Kushina and her aggressive clan HOMRA find themselves caught up in the Green King’s games. Amidst the chaos, Kurou Yatogami and Neko are left vulnerable while their beloved friend, Yashiro Isana, the Silver King, remains missing. K: Return of Kings tells the struggle of the remaining clans against the Green King’s formidable forces as one final king appears. [Written by MAL Rewrite]

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

During his summer vacation, middle school student Nagasumi Michishio travels to the Seto Inland Sea. One day, while swimming at Mio Sun Beach, his leg suddenly cramps. No one is close enough to notice his desperate screams for help, and so he sinks into the ocean, where he is left to drown alone. Just as he loses consciousness, however, a mermaid appears and saves his life. That night, Nagasumi is visited by his savior, a girl who introduces herself as Sun Seto—a mermaid from a yakuza family. As it turns out, under mermaid law, a mermaid whose identity is revealed to a human must be punished by execution. To avoid this harrowing outcome, the Seto family propose a solution: Nagasumi must marry Sun or die at the hands of Gouzaburou, Sun's father and boss of the Seto clan. Faced with no other option, Nagasumi takes her hand in marriage. Now, the newlyweds face the difficult task of keeping their relationship secret. Between Gouzaburou's unending attempts on Nagasumi's life and the eccentric antics of a slew of antagonists, a genuine and innocent love blossoms between the pair as they adapt to their new life. [Written by MAL Rewrite]