Lucia's guardian who serves as her guide. Hippo accompanies Lucia in her search for her pink pearl, and is among those who voice disapproval of her relationship with Kaito. He is also polite, always putting -さん (-san) after every name, even when angry.

Spoiler

At first, he is shown as Lucia's pet penguin, but later on, it is revealed that his real form is that of a cute human boy, but he is embarrassed of how he looks since it's so different from other creatures of the sea. Under his human form, he falls in love with Yuri. And Yuri also loves his human form.

Spoiler

Later on, he also transforms on a creature called Hippocampus.