Aqua Knight (水中騎士, Akua Naito) is a Japanese manga series written and illustrated by Yukito Kishiro.

It's a tale about Ruliya, a female orca-riding knight, making an epic journey through the aqueous world of Marmundo.

Tagmec, knight of the Underworld, emerges from the sea to claim the old man, but not before Ruliya promises to rescue the boy and the light.

Pinoque, a fairy friend from her childhood, returns to her to aid in her quest, and she sets out after Ashika and the light sphere with renewed purpose.

He escaped Zygote in a zeppelin, taking with him Zykey, a young woman whose mysterious Nil-nil disease prompted him to become the genius he is today.

Ruliya manages to beat Alcantara's masterful swordsmanship in the end, but they emerge from the sea to find that sinister, demonic powers have been plotting to take the sphere for themselves.

A great battle against the metal demon ensues, and only with the help of the forces of the Underworld Knight Tagmec can Ruliya finally defeat it with her magic blade.

Like all knights of Marmundo, she rides an orca and wears a massive, magical armor that increases her strength and allows her to fight under water.

Ashika, a young boy who has grown up on a small island with his father Arrabarus, is an impulsive, emotional child who is as naive and uneducated as he is optimistic.

Arrabarus, a giant, scarred old man, claims the title of king of the lighthouse island, but has a history as a great aqua knight.

Alcantara, a wandering genius, nobleman, and inventor, has fled his homelands in search of the elixir of life, of which he believes Niselle is an ingredient.