The central twist of "Light Shop" is that nearly all the main characters visiting the shop are the spirits of passengers who were on a bus that crashed; they are all in a coma, existing in a shared purgatory. The mysterious and sometimes frightening events of the first half are revealed to be the interactions between these lost souls and other entities in this liminal space. The 'strange' characteristics of certain people—like Lee Ji-young's unusual fingernails or another character's constant chill—are signs that they are not among the living.
Jung Won-young, the shopkeeper, is not a supernatural being by origin, but the soul of a man who died in a building collapse decades prior. He made a deal to run the shop in exchange for a chance to save his daughter, who was also dying in the accident. The finale reveals that Jung Yu-hee, the distraught mother of the high school student Hyun-ju, is actually Won-young's long-lost daughter, whom he finally gets to meet again. Yu-hee also died in the bus crash, creating a tragic family loop. Won-young ultimately succeeds in sending his granddaughter, Hyun-ju, back to the world of the living.
Detective Yang Sung-sik doesn't just wake up from his coma; he awakens with the ability to see the dead, having been 'chosen' to become a new guide for lost souls, taking over from another spirit he was investigating. The most tragic fate is that of Lee Ji-young. After successfully guiding her boyfriend Hyun-min back to life, he awakens with amnesia and forgets her completely. Her all-consuming love, now unanchored and unrecognized, curdles into sorrow and resentment, trapping her as a vengeful ghost bound to him forever.