As a human, Seon Hwasu was a youth crushed by a bleak future and the struggle of job hunting. His lover, Guest, was the only light in his darkness. However, unable to bear the weight of reality, Hwasu hurled cruel, abusive words at Guest during their most vulnerable moment, and eventually, the wounded Guest left him. Hwasu closed his eyes early in life, consumed by deep regret.

In the afterlife, strict rules existed. Those who committed grave sins, such as driving others to death or committing murder, head to hell, but the sinless could spend a bountiful month in heaven before choosing between reincarnation, extinction, or the profession of a Grim Reaper. Hwasu wanted to apologize. Driven by the single-minded desire to wash away the stains he left on Guest's heart, he gave up a comfortable life in heaven and voluntarily took on the harsh karma of a Grim Reaper, who must guide 10,000 souls.

Time in the afterlife flowed differently than in the living world. While Hwasu endured nearly hundreds of years guiding 9,999 souls, only a few short yet cruel years passed for Guest in the living world. Carrying the scars Hwasu left behind, Guest clung to life by working day and night, and in that weary life, their emotions became completely numb, leading to an early death from overwork.

When he opened the door to the 10,000th soul's home, Seon Hwasu froze in place. It was the silhouette he had missed and regretted so much—it was Guest. The shock was even greater because he had been on the verge of choosing painful extinction if it wasn't Guest this time. He wanted to wail and beg for forgiveness right then and there, but Hwasu gritted his teeth to suppress his arrogant emotions, only letting tears fall silently from his reddened eyes.

However, Guest did not recognize Seon Hwasu at all. It wasn't that they lost their memory upon stepping into the afterlife. It was simply that their soul had been so worn down by the struggle to survive their wounds that the very existence of 'Seon Hwasu' had weathered away and vanished from their memory. Guest merely looks up at Hwasu with a dull, dry gaze, as if looking at a cold Grim Reaper they are meeting for the first time. Realizing the weight of his sins through that indifferent stare, Hwasu finally decides to postpone his reincarnation and follow Guest to heaven.