Hippopotamus is the shadow belonging to Bouquet in the anime Blue Dragon: Trials of the Seven Shadows. This character is exclusive to the anime adaptation and does not appear in the original Blue Dragon video games. Throughout the series, Hippopotamus is established as a shadow that is not a strong fighter, often displaying a timid and somewhat cowardly nature, preferring to hide when dangerous situations arise. Despite this lack of combat prowess, Hippopotamus possesses a kind heart and is deeply dedicated to Bouquet's well-being, consistently looking out for her safety whenever a battle begins.

The primary and most notable ability of Hippopotamus is transformation. By merging with Bouquet, Hippopotamus can change her appearance into anything she desires, frequently using this power to create disguises that allow the group to gather information or move unnoticed. This ability is demonstrated when Bouquet transforms to resemble a village woman to investigate strange occurrences. In another instance, Hippopotamus even dresses up as a superhero called Hippopotaman to entertain a crowd and manage a chaotic situation involving Blue Dragon.

As the series progresses and the characters face more powerful enemies, Hippopotamus gains additional capabilities. After unlocking ancient ruins, Hippopotamus develops the power of mimicry, allowing it to copy the attacks that hit it. This power is even shown to extend to transforming into a Black Shadow Type Three robot to use its abilities. Later in the second series, a character named Noi awakens an even more powerful technique. This ability allows Hippopotamus and Bouquet to transform together into a glowing pink ball of energy. When another shadow, such as Shu's Blue Dragon or Marumaro's Saber Tiger, absorbs this ball, it fuses with them, granting the recipient a near-perfect armored form and a tremendous increase in power. This combination technique becomes a crucial asset in battles against formidable foes.

In the context of the story, Hippopotamus serves as Bouquet's partner, enabling her to contribute to the team's missions in unique ways beyond direct combat. Their role is often tactical, using disguises for espionage and merging with the group's heavier hitters to turn the tide of major conflicts. This relationship highlights the bond between Bouquet and her shadow, where his protective instincts and her resourcefulness make them a vital part of the group.