Before becoming the soft-spoken kindergarten teacher and shojo manga enthusiast at Black Kindergarten, Luke Smith was a London police officer. The spin-off, Kindergarten WARS -LUKE-, chronicles this tragic past, revealing the events that led to his life as a convicted criminal.

The story follows a younger, idealistic Luke, who is full of a vibrant sense of justice. He works alongside his mentor and superior, Oliver, and dreams of a future with his beloved girlfriend, Tina. Their police work leads them to clash with Red Dawn, a dangerous and mysterious cult rumored to be seeking the fountain of youth by abducting and sacrificing children. Luke and Oliver successfully arrest several members of the organization, but this action triggers a devastating retaliation.

In a single, catastrophic event, Luke loses everything. His trusted superior Oliver, his cherished colleagues, and most tragically, his fiancée Tina, are all killed. Tina loses her life protecting Luke. Consumed by guilt and despair over failing to protect those he loved, Luke is left a shattered man. His trauma is compounded when he is falsely accused of murdering his colleagues, a crime he did not commit. As a result, Luke becomes an inmate, designated as prisoner number 225.

The narrative details how this broken former officer eventually finds his way to Black Kindergarten, the world's most secure nursery for the children of the global elite. There, other ex-convicts work as specialized teachers in exchange for reduced sentences. Luke is assigned to the Chrysanthemum class alongside his partner, Sylvia Scott. While the main series focuses on action and romantic comedy, this spin-off is a serious human drama and tragedy that explains Luke’s personality. It reveals the sorrowful reasons behind his quiet demeanor, his love for sweet foods like his favorite nikujaga, and his encyclopedic knowledge of shojo manga, which is shown to be a nostalgic link to a past happiness he lost. The volume concludes by leading directly into Luke’s fate in the primary storyline, including his final confrontation with the powerful adversary Aoba.