Dera Mochimazzui is a talking bird who serves as a noble attendant to the royal family of a distant, tropical land. He arrives in the Usagiyama Shopping District on a mission to find a suitable bride for the prince, but his plans are derailed when he develops an insatiable appetite for mochi, the traditional Japanese rice cakes that are the specialty of the area. His constant consumption of mochi causes him to gain a significant amount of weight, transforming him from a relatively slim bird into a round, egg-shaped figure roughly half the size of a human girl, which ultimately leaves him unable to fly more than short distances. He has white feathers with pink ends on his wings, a strand of feathers on his head that ends in pink, and small legs and claws which he often poses in a way reminiscent of a fashion model.

In terms of personality, Dera is pompous, bossy, and dramatic, with an inflated sense of his own importance due to his royal status. He speaks with an exaggeratedly formal and eloquent tone, often addressing others as young man or young girl. Despite his proud and self-absorbed exterior, he is generally good-natured and demonstrates a surprising sharpness in noticing the feelings of others, occasionally offering valuable support and advice. He is something of a womanizer, constantly hoping to attract romantic attention; one of his running gags is his belief that any girl who sneezes on him is expressing affection. He develops a noticeable, one-sided crush on a girl named Shiori Asagiri, whom he finds lovely and elegant, and he persists in showering her with compliments despite her indifference. He also shows a less admirable side when his curiosity gets the better of him, such as when he peeks into the girls' side of a bathhouse.

Dera's role in the story is primarily that of a comedic mascot and an outside observer who provides commentary on the everyday lives and romantic entanglements of those around him. He becomes a freeloader in the home of the main character, Tamako Kitashirakawa, whose family runs a mochi shop, and he is often simply called Bird by her family because his full surname sounds like the Japanese phrase for bad-tasting mochi. His key relationships include his dynamic with Tamako, whom he sees as a young girl who may harbor feelings for him, and his interactions with Mochizō Ōji, Tamako's childhood friend. Dera becomes aware of Mochizō's crush on Tamako and, despite Mochizō's initial discomfort, sometimes offers him love advice and assistance. He also has a relationship with Choi Mochimazzi, a young fortune teller from the same royal court; he teases her but is also visibly terrified of her temper, addressing her respectfully as Choi-sama when she is angered.

Throughout the series, Dera shows little formal development regarding his primary mission, as his love for mochi and his comfortable new life in the shopping district keep him firmly grounded. However, he does demonstrate moments of genuine appreciation for his found family. For instance, he is shown to miss Tamako when he briefly returns to his home island. His most notable ability, aside from speaking fluent Japanese, is his function as a communication device for the prince. His body contains a system that allows him to project messages and images from his beak or eyes, though this often activates only when he is unconscious, leaving him with no memory of the transmissions. Despite his failures as a royal attendant, his surprisingly insightful nature and his role as a catalyst for helping others confront their own feelings make him a unique and memorable presence in the community.