"Earthian" is a science fiction manga series set in a future where humanity is divided into two groups: the Earthians, who are ordinary humans, and the Evolians, a genetically superior race created by advanced technology. The story primarily revolves around the interactions between these two groups, exploring themes of coexistence, prejudice, and identity.

The narrative centers on Chihaya, an Earthian, and Kagetsuya, an Evolian, who work together as a pair of "Angels" tasked with observing and evaluating humanity. Their mission is to determine whether Earthians are worthy of continued existence, as the Evolians consider themselves the next step in human evolution and debate whether to eliminate or preserve the Earthians. Chihaya, despite being an Earthian, is chosen for this role due to his exceptional abilities and resilience, while Kagetsuya, an Evolian, serves as his partner and protector.

As the story progresses, Chihaya and Kagetsuya encounter various individuals and situations that challenge their perspectives on humanity. Chihaya's unwavering belief in the potential for good in Earthians contrasts with Kagetsuya's more detached and critical view, shaped by his Evolian upbringing. Their partnership evolves into a deep bond, blending elements of camaraderie and romance, which becomes a central emotional thread throughout the series.

The manga delves into the ethical dilemmas faced by the Angels as they witness both the kindness and cruelty of humanity. Key arcs involve encounters with other Angels, conflicts within the Evolian hierarchy, and the discovery of hidden truths about the origins of the Evolians and their relationship to Earthians. These revelations force Chihaya and Kagetsuya to confront their own identities and the broader implications of their mission.

Supporting characters, such as the enigmatic Evolian leader Michael and other Angels like Raphael and Uriel, add complexity to the narrative, highlighting the internal struggles and power dynamics within the Evolian society. The series also explores the lives of ordinary Earthians, whose actions and choices are scrutinized by the Angels, further emphasizing the moral ambiguity of the central conflict.

"Earthian" combines elements of science fiction, romance, and philosophical inquiry, presenting a thought-provoking exploration of humanity's flaws and potential. The interplay between Chihaya and Kagetsuya, along with the broader societal tensions, drives the narrative forward, creating a compelling and emotionally resonant story.