The successor and branch manager of the Himeya Company—one of the many Undine associations housing female gondoliers—Aika S. Granzchesta surprises everyone when she rejects tradition and refuses to inherit the company's legendary gondola. Aika's apprentice Azusa B. McLaren, unable to wrap her mind around her mentor's unexpected decision, confronts her directly but to little effect. To better understand her reasoning, Azusa and her fellow Undines secretly plan to arrange a meeting with Aika. With the much-awaited winter days in sight, accompanied by the tranquility and sublimity of Neo-Venezia, Aika reminisces about her journey as an Undine that forged her into the person she is today. As she vividly remembers all those invaluable experiences of the past, she trusts they will continue to guide her into the unknown yet boundless future.

A completely new feature-length animation commemorating the 100th anniversary of Shigeru Mizuki's birth. The story of Kitaro's father is revealed for the first time.

In the series' backstory, 102,000 years ago in a place that would be modern-day Mexico, it started with a mysterious but powerful race with incredibly long lifespans and the ability to absorb life forces from plants and animals, although they had the disadvantage of being easily disintegrated if exposed to sunlight and thus lived underground instead. Kars, an underground-dwelling humanoid being known as a Pillar Man, created a stone mask which grants immortality by absorbing life energy to conquer the sun (which kills his kind). However, the stone mask cannot penetrate his head and unlock Kars' true potential. As he tirelessly slaughtered things for blood to activate the stone mask, his tribe begins to fear Kars for his obsession. When his tribe says Kars must be killed, Kars is angered and questions them if they want to conquer the sun. If they objected, Kars would say they will die. As his tribe attempts to kill him, Kars and his companion Esidisi fight back. He slaughtered all but four of the tribe.

While the funeral of the assassinated Prince Edward, who was the first in line to succeed the throne, is being held, the nobles of the Kingdom of Albion discuss topics such as whether the second-in-line Princess Mary or the third-in-line Duke of Arkham, Prince Richard, will succeed the throne, and how the Duke of Normandy will act. The Duke of Arkham asks Princess if she will side with him or the Duke of Normandy. While wishing to change the world so that all people are equal, Princess is shaken by the Duke of Arkham, who is the mastermind behind Edward's assassination. Meanwhile, Ange and Dorothy are given a mission to infiltrate as Mary's maids and investigate the state of the royal family by the Commonwealth's control. Mary is crushed and exhausted due to the pressure of becoming first in line to the throne. As chaos surrounds the succession to the throne, the Duke of Arkham's plot finally begins to unfold. The darkness writhing in the Kingdom of Albion begins to swallow up Team White Pigeon.