She comes to Penacony as a "Galaxy Ranger" and attends the family's banquet. Although she keeps her distance from the protagonist, she will help them when necessary. In the story, she reveals her true identity as an Emanator of Nihility: Nothingness.

On the surface: a cold and silent intergalactic ronin, an ascetic imperial maiden. She has embarked on a lonely journey for vengeance, but still seems to have goodness in her heart.
In reality, she is an IX Emanator of Abundance, a "Self-Annihilator" born out of nothingness, with no memory or past, wielding a sword that cuts off the path of life.

Firefly, formerly known as AR-26710, was born in an incubation pod of the Falakor Galaxy. As a genetically-modified baby, fate left her with only one future: To become the pilot of the Molten Knight "Samuel-IV" (referred to as Sam), and to join the endless war between humans and The Swarm.

But before Firefly set foot on the battlefield, her fleet was ambushed. The overwhelming argenites destroyed the ship, wiping out the army in space. Decades later, the drifting wreckage was recovered by the Stellaron Hunters. After waking up from a deep sleep, she was told that her old planet had perished in the catastrophe caused by the Antimatter Legion. But, the centuries-long war between humans and insects was finally proclaimed as over by a third party from outside.

So Firefly took the Molten Knight armor and joined the Stellaron Hunters. Her life was on a countdown, but Elio says that this journey will teach her how to live. Elio stopped there, the answers to her questions are for Firefly to find out herself. So before arriving at her predestined conclusion, despite only having a fleeting lifespan akin to that of an actual firefly, she is willing to experience anything and everything.

 Due to gene editing, Firefly's aging is different from that of ordinary people. One day, she will rapidly age and die. Compared to long-life species, she is a short-life species.

The Molten Knight is actually a weapon made by humans using argenite husk. Whoever pilots it will be affected by the Path of Propagation, and their body tissue and mental state will be corroded, resulting in mutations until death.

One of the leaders of The Family. After Hanunu (the first ruler of Penacony), died of illness, Sunday was invited by the Oak Family to help find a solution to the hypersomnia mutation crisis 

Sunday's proposed solution to the mutation was to use a Stellaron that had been kept under the stewardship of Hanunu. He proposed to activate the Stellaron in order to create a "wedge" in the Dreamscape — a creation of the Enigmata — thereby stabilizing the local area of the Dreamscape. This would enable Penaconians affected by hypersomnia to travel through the Dreamscape and seek refuge, thus allowing them to return to their normal sleep cycle in reality.

The six major families convened to vote on the proposal, which ended in a three-to-three tie. At the instigation of Chachakuka, they tabled the proposal for the time being and moved on to consider other solutions. The next Amber Era coincided with the death of Chachakuka, and the Oak Family became the new rulers of Penacony, who once again turned their attention to the Stellaron... This time, in a ceremony supervised by Sunday himself, Hanunu's orphaned son, Misha, activated the Stellaron and became the Dreamscape Lord, after which the Dreamscape enveloping Penacony gradually became more peaceful. (When he made his wish to the Stellaron, Misha shared some of his authority over the Dreamscape with Watchmaker, which explains the origin of Watchmaker's legacy in the Dreamscape).

The Nightingale Family and the Iris Family responded to the call, and Penacony eventually became the "Planet of Festivities". Mihail realizes that Penacony is heading for a different kind of nightmare, and ultimately decides to seek out power and negotiate with The Family's representative on Penacony — Sunday. Meanwhile, Sunday is eagerly searching for Mihail from the Dreamscape, who is the biggest obstacle to The Family's expansion, and must be eradicated.

On the surface, Sunday is an excellent leader: He seems reasonable, hardworking, an absolute moral model to outsiders, and a natural leader and judge. In the face of (what Sunday considers) virtue, he will offer unconditional acceptance with a big heart. In the face of evil, he will rain down merciless punishment.

On the inside, Sunday is not nearly as kindhearted as he seems. A control freak by nature, he takes pleasure in controlling the behavior and thoughts of others, which is how he became a Family spokesperson. He will coerce, discipline, and even punish others with great effectiveness in order to satisfy his own selfish desires. ( This is not directly shown in the story ) 

Be that as it may, Sunday is not an absolute hypocrite: His great empathy and compassion are real, and he is thus able to guide the public and indeed lead The Family and Penacony upwards for many an Amber Age. He will heartily rejoice in the joys of others and grieve over their sorrows — but that doesn't stop him from fulfilling his selfish desires with a strong hand.