Rion Vale is an F-Rank hunter, the weakest rank in a world ruled by magic. Treated as a burden, he enters a “safe” dungeon hoping to prove himself, only for the gate to seal behind him. Inside, time flows differently and death forces him to restart. The monsters evolve endlessly, growing stronger every cycle. Rion, with no magic, survives only through instinct, will, and the natural energy hidden in his body. What should have been a simple mission becomes a hundred years of nonstop battle. When he finally escapes, only five hours have passed outside. Still labeled F-Rank, Rion returns unaware that he has become stronger than every hunter and monster alive.