Fuku-chan is a character who appears in the second story arc of the series, known as the Pure arc. He initially presents himself as a small, pet white bird kept in a cage by the human girl Mikaru Amagi. This appearance, however, is a disguise. His true form is that of a tiny, ancient being with a bird-like body and the head of a girl, characterized by deep pink or magenta hair, black eyes, and an angel-like ring floating above its head. Despite a small stature, approximately thirty centimeters tall, Fuku-chan is a being of great age, having existed for over ten thousand years.

Contrary to his cute and seemingly harmless appearance, Fuku-chan possesses a cold, calculating, and manipulative personality. He is described as sly, arrogant, and extremely annoying by those who must deal with him, frequently taunting the other servants of his master, particularly the Black Beauty Sisters, whom he often calls failures. His speech is punctuated by a distinctive laugh or verbal tic that sounds like "pu pu pu" in the anime adaptation. He is ruthless in pursuing his goals, willing to sacrifice anyone or use any means necessary without hesitation.

Fuku-chan's primary motivation is the resurrection of the ancient race to which he belongs, a species of beings that once ruled the Earth before humanity emerged. He is not a loyal servant but rather the secret mastermind behind the season's primary antagonist, Mikeru. Fuku-chan acts as Mikeru's messenger and right-hand to his servants, but his true function is to control and manipulate Mikeru, who is actually a clone created by human technology from a fossil of an ancient emperor. He is the one primarily responsible for orchestrating the events of the plot, including manipulating Mikaru's father into using his daughter as a vessel to revive Mikeru.

Fuku-chan's key relationships are defined by deception and utility. He uses Mikaru by posing as her harmless pet to monitor her. Among Mikeru's servants, he holds the Black Beauty Sisters in contempt, though he seems to have a slightly better, if still nervous, relationship with their comrade Alala, for whom he harbors a bit of a crush despite her tendency to set him on fire for his annoyance. He relies on the more competent servants, Lady Bat and Lanhua, to carry out important missions. The most significant relationship is with Mikeru himself. For most of the story, Fuku-chan acts as his subordinate, but it is eventually revealed that he has the ability to possess and order Mikeru around, doing so when the clone loses the will to fight. In this sense, he is the true primary antagonist.

Development for Fuku-chan occurs in the final episodes and chapters, where his role as the hidden puppeteer is fully exposed. When Mikeru rejects his mission of destruction and the ancient humans appear to apologize for burdening him, Fuku-chan ultimately leaves the world of the living with Mikeru, returning to the afterlife or dream world where his fellow ancient beings reside.

In terms of abilities, Fuku-chan's primary power is his duplicity and skill at manipulation. He can change his form between a realistic-looking pet bird and his true, chibi-like angelic appearance. He is also explicitly shown to possess the ability to dominate and control the body of another being, which he uses to take command of Mikeru directly. Beyond this, he serves as a messenger and liaison, capable of bestowing power upon other servants like Alala to help them in their tasks. He is also incredibly durable, being frequently subjected to physical abuse—such as being smacked, swung around, or even set on fire—by his allies without lasting harm.