A young sphinx cub created by Osamu Tezuka and Sanrio from the Unico manga series. Piro/Marusu (referred as "The Sphinx's Daughter/Son" in the English dub of "Unico in the Island of Magic") is a young sphinx that Unico encounters as he and Cherry/Cheri are finding ways to defeat Lord Kuruku. Despite his/her short temper, he/she's very nice around Unico and cheers him up when he thinks Cherry/Cheri won't love him anymore. His/Her relationship with Unico is notably different in the original manga series in a different location the titular unicorn meets him/her.

In the original manga, the character is known as Piro and a male, while the character's animated appearance in "Unico in the Island of Magic" never states the exact gender for the Piro/Marusu. In the manga, he debuts in the chapter "The Tale of The Fangs of Athens" where he befriends Unico after his mother takes the young unicorn into a cave after failing to solve her riddle. The young sphinx rejects his mother's offer since he finds the idea of eating unicorns disgusting. While his mother's away, he and Unico form a close friendship with her son deciding to trick his mother into thinking he ate the unicorn. After Unico breaks the news that his mother was killed by Oedipus, Piro ends up adopted by Unico where he learns to be a "Brave and Strong Sphinx" and the importance of self-defense.

In "Unico: Awakening", Marusu gets kidnapped by Venus in order to seek further information about Unico's powers and whereabouts. In the English-language reboot series, the character is a female sphinx and given an Egyptian inspired redesign where she wears yellow eyeliner and headdress (hidden behind her bangs) which contains a third-eye. Marusu is also depicted with Turquoise color fur and dark blue hair and tail tip which she shared from her mother.