"Shūkyoku Engage" is a manga series that blends elements of action, fantasy, and psychological drama. The narrative centers on a world where humanity faces extinction due to the emergence of monstrous entities known as "Engage." These creatures are born from human despair and negative emotions, manifesting as physical threats that ravage society. To combat this existential crisis, a specialized organization called the Engage Bureau is established, tasked with identifying and neutralizing these entities before they can cause further destruction.

The protagonist, a young man named Kaito, becomes entangled in this struggle after a personal tragedy involving the Engage. He possesses a unique ability to "engage" with these creatures, allowing him to enter their inner worlds and confront the emotional cores that sustain them. This ability, however, comes at a cost, as it requires Kaito to confront his own psychological scars and vulnerabilities. Alongside Kaito is a diverse cast of characters, each with their own motivations and connections to the Engage phenomenon. These include members of the Engage Bureau, such as the stoic and determined leader, Rina, and the enigmatic scientist, Dr. Kuroda, who seeks to understand the origins of the Engage.

The plot unfolds through a series of missions where Kaito and his allies face increasingly complex and dangerous Engage, each representing different facets of human despair, such as grief, guilt, and fear. As the story progresses, it delves into the origins of the Engage, revealing a deeper connection between their existence and the collective psyche of humanity. Themes of redemption, the nature of despair, and the resilience of the human spirit are explored as Kaito and his companions grapple with both external threats and their own inner demons. The narrative maintains a balance between high-stakes action and introspective character development, creating a compelling and multifaceted story.