Wandayū serves as an envoy from planet Mal, tasked with announcing Eri Kasuga's selection as the future bride for Prince Lulealv. He is a dog-like alien sporting brown fur, black ears, and eyes typically concealed by drooping eyelids that reveal themselves when he is surprised or angered. His appearance features a circular facial area, exposed hands and feet, and a brown-tipped tail. Eri refers to him affectionately as "Grandpa Wanda," reflecting his elderly demeanor. His primary mission involves delivering gifts and messages from Prince Lulealv to Eri, though she consistently rejects these offerings and the marriage proposal itself. To persuade her, Wandayū devises elaborate schemes, often involving Rube Goldberg-style contraptions prone to spectacular malfunction, typically resulting in comedic mishaps like eggs striking Mr. Kasuga's face. He announces his arrivals by shouting "Congratulations!" while showering confetti and streamers, inevitably annoying Eri and creating messes she must clean. His relationship with fellow envoy Chinpui is collaborative yet occasionally contentious when Chinpui disobeys directives. Together, they counteract external threats to Eri, such as rival alien Darusa's attempts to eliminate her as a marriage candidate or Majino-san's aggressive persuasion tactics. Wandayū actively sabotages Eri's bond with her classmate Uchiki Shō to prevent their relationship from jeopardizing the prince's future lineage. Like other inhabitants of planet Mal, Wandayū wields reality-altering magic activated by shouting his name, though these powers often yield chaotic or unintended consequences. His persistent interventions and flawed inventions underscore his role in generating comedic conflict within the narrative.