The Hunter's One Night summary:

In a world where dungeons appear randomly, some humans manifest as Hunters.In return for serving the nation for ten years as a mandatory requirement, the siblings of Hunters are exempted from enlisting in the South Korean military. Due to this, adopting a child with the potential of becoming a hunter has become a trend for the wealthy.Yeonwoo wasn’t any different than those typical cases. He was adopted, became a Hunter, and joined the military in the place of his younger stepbrother, Jungwoo, who was only a year younger than him. In Yeonwoo’s fifth year serving in the military, an unidentified dungeon appears near the university that Jungwoo attends. Yeonwoo voluntarily throws himself into that dungeon.Therefore, Mo Yeonwoo, as the elder brother and Hunter who enlisted on behalf of Jungwoo, was obligated to protect Mo Jungwoo’s peaceful life in any way he could. The day before enlisting, even with Jungwoo struggling to refuse, Yeonwoo pinned down Jungwoo through brute force, sucked his dick, and shoved it into his own hole.He had to pay the price. Even if it cost his life.