"Bye Bye, Earth" is a fantasy anime series set in a world where humans coexist with anthropomorphic animal beings, known as "Beast Humans." The story centers on Belle Lablac, a young girl who is the only human in a society dominated by Beast Humans. Her unique status makes her an outcast, and she is often met with fear and prejudice. Despite this, Belle is determined to find her place in the world and uncover the truth about her origins, as she has no memory of her parents or why she is the sole human in this society.

Belle wields a mysterious sword that seems to have a will of its own, granting her extraordinary combat abilities. This sword becomes a key element in her journey, as it ties into the larger mysteries of the world. As she travels, Belle encounters various factions and individuals, each with their own agendas and beliefs about the coexistence of humans and Beast Humans. Among these is a group of Beast Humans who view her as a threat to their way of life, while others see her as a potential savior or a symbol of change.

The narrative explores themes of identity, belonging, and the struggle for acceptance in a divided world. Belle's journey is both physical and emotional, as she grapples with her loneliness and the weight of being different. Along the way, she forms bonds with a diverse cast of characters, including Beast Humans who challenge societal norms and humans who have hidden themselves away. These relationships shape her understanding of the world and her role within it.

The plot is driven by Belle's quest to uncover the truth about her existence and the origins of her sword, which is revealed to be connected to ancient conflicts between humans and Beast Humans. As she delves deeper, she uncovers secrets about the world's history, including the reasons for the near-extinction of humans and the rise of Beast Humans as the dominant species. The series balances action, mystery, and character development, creating a layered narrative that keeps viewers engaged.

"Bye Bye, Earth" presents a richly detailed world with complex social dynamics and moral ambiguities. The story avoids simplistic dichotomies, instead portraying a society where both humans and Beast Humans are capable of both good and evil. Belle's journey is one of self-discovery and resilience, as she navigates a world that often rejects her while striving to find her purpose and forge her own path. The series concludes with a mix of resolution and open-ended questions, leaving room for further exploration of its themes and characters.