"Sin Strange Plus" is a science fiction anime series set in a dystopian future where humanity is on the brink of extinction due to a mysterious phenomenon known as the "Collapse." This event has caused the collapse of advanced civilizations, leaving behind fragmented societies struggling to survive in a world overrun by hostile entities called "Aberrants." These creatures, born from the Collapse, are manifestations of humanity's darkest emotions and fears, posing a constant threat to the remnants of civilization.

The story centers on a group of individuals known as "Striders," genetically enhanced humans designed to combat Aberrants. The protagonist, Kael Ardent, is a former elite Strider who has abandoned his duties after a tragic mission resulted in the loss of his team. Haunted by guilt and disillusionment, Kael lives as a drifter until he encounters a young girl named Lira, who possesses a unique ability to manipulate the Collapse's energy. Lira becomes a target for both Aberrants and a shadowy organization known as the "Eclipse Syndicate," which seeks to exploit her powers for their own agenda.

Reluctantly, Kael takes on the role of Lira's protector, forming an uneasy alliance with a rogue Strider named Selene Veyra, who has her own reasons for opposing the Eclipse Syndicate. Together, they navigate a perilous world filled with moral ambiguity, uncovering secrets about the Collapse, the origins of Aberrants, and the true purpose of the Striders. As they delve deeper, they encounter other factions, including a resistance group fighting against the Syndicate's tyranny and remnants of the old world's military, each with their own motivations and interpretations of the Collapse.

The narrative explores themes of survival, redemption, and the consequences of humanity's hubris. Kael's journey is one of self-discovery as he grapples with his past failures and the ethical dilemmas of wielding power in a broken world. Lira's innocence and unique abilities serve as a catalyst for change, challenging the characters' beliefs about the Collapse and their roles in shaping the future. The series balances action-packed sequences with introspective moments, creating a layered story that examines the human condition in the face of existential threats.