A 35-year-old adventurer named Koosuke Igami holds the lowest Class 3 ranking and has been serving his mandatory term for nearly five years, with only three months remaining until he can finally retire. He currently finds himself as a mere placeholder member on a team of talented but inexperienced high-class adventurers. The world itself was transformed when an experiment to generate energy went disastrously wrong, tearing open a portal to another dimension filled with monsters. In the aftermath, certain humans awakened supernatural abilities similar to those creatures and became known as the Awakened Ones, obligated to serve for five years once their powers manifested. Despite being dismissed by others as an unremarkable middle-aged man who simply fills out the party's numbers, Koosuke is in truth a legendary adventurer of immense hidden power. His unassuming facade conceals abilities far beyond his low rank, and he soon finds himself in the unexpected role of mentor, tasked with raising and training a heroic young girl alongside other gifted companions. What begins as a countdown to retirement transforms into a journey of hidden identities, the gap between perception and reality, and the bonds formed between a jaded veteran and the promising next generation of heroes.