Akudaikaan reigns as the primary antagonist throughout most of *Futari wa Pretty Cure Splash Star*, the imposing ruler of the evil organization Dark Fall. His core objective is seizing control of the World Tree, the life source of all worlds. He captures six of the seven fountains nourishing the tree, relentlessly pursuing the final, elusive Fountain of the Sun. He dispatches subordinates to find this fountain and capture the fairy spirits Flappy and Choppy.

Visually, he manifests as a massive, shadowy entity draped in dark robes within a cavern. Piercing, glowing eyes—depicted as yellow or red—shine from the darkness concealing his form. His design resembles a demonic figure or an Edo-period Oni mask. His name combines the Japanese words "aku" (悪, "evil") and "daikan" (代官, a historical local administrator title), foreshadowing his role.

He commands Dark Fall with strict authority, frequently scolding minions like Karehaan for failures and threatening annihilation for incompetence. His intolerance for disloyalty leads him to banish the Kiryuu sisters, Michiru and Kaoru, after they defy orders to eliminate Pretty Cure and seek freedom. Despite his fearsome reputation, direct confrontations are rare; he demonstrates overwhelming power early on, effortlessly defeating Cure Bloom and Cure Egret from his throne.

A pivotal revelation near the series' end redefines him: Akudaikaan is exposed as a puppet created and controlled by his seemingly subservient aide, Goyan. Goyan engineered Dark Fall and Akudaikaan to corrupt and destroy the fountains, aiming to annihilate all existence. After Pretty Cure nearly defeats Akudaikaan, Goyan discards him, revealing his true form and obliterating Akudaikaan to assume direct control. This twist establishes him as the franchise's first "man behind the curtain" figurehead villain masking the true antagonist.

His narrative arc concludes with this destruction.