Hai no Sekai wa Kami no Me de Irozuku ~Ore dake Mieru Status de, Saijaku kara Saikyou e Kageagaru~

In a world transformed by the sudden emergence of dungeons, humanity has awakened to magical abilities. However, an individual's strength is strictly dictated by the amount of magic they possess from birth. Amachi Kai was born with barely any magical power, leaving him at the very bottom of the explorer hierarchy. Despite his severe disadvantage, he continually risks his life inside dungeons, working as a low-ranking conqueror solely to fund the expensive medical treatments required by his younger sister, Nagi, who suffers from a grave illness. Kai’s fragile routine shatters when Nagi’s condition takes a sudden and drastic turn for the worse. The cost of saving her life skyrockets, demanding an astronomical sum of money that his usual dungeon runs could never provide in time. Pushed to the brink of despair and stripped of safer alternatives, Kai makes a desperate gamble. He volunteers for the highly dangerous investigation of a completely uncharted dungeon—a perilous expedition that promises an enormous financial reward to those who survive it. With his sister's life hanging in the balance, the weakest explorer steps into the unknown, driven by a resolve that defies his limitations.