The central plot twist of "Hotel Del Luna" is the true story behind Jang Man-wol's betrayal. For over 1,000 years, Man-wol believed that Go Chung-myung, the captain she loved, betrayed her and her people to marry Princess Song-hwa, leading to their deaths. This belief fuels her immense grudge. However, the series reveals that Chung-myung's actions were a desperate act of sacrifice. He orchestrated the 'betrayal' to save Man-wol's life, as she was the only one spared. Wracked with guilt, he allows himself to be killed by her and then spends the next millennium as a firefly, silently staying by her side, unable to move on.
This revelation re-contextualizes Man-wol's entire existence; her curse was built on a misunderstanding. She wasn't just waiting for revenge, she was unknowingly being watched over by the man she thought had wronged her. Gu Chan-sung is eventually revealed to have been connected to Man-wol in a past life as well. The finale sees Man-wol finally understanding Chung-myung's sacrifice. She forgives him and Princess Song-hwa's reincarnation, and is escorted by Chung-myung across the Sanzu River bridge, finally freeing both of their souls. Gu Chan-sung fulfills his promise to send her off, choosing not to use medicine that would stop him from seeing ghosts, thus keeping her world with him. The hotel vanishes as Man-wol's penance is complete, and the remaining staff—Kim Seon-bi, Choi Seo-hee, and Ji Hyun-joong—all find closure and move on to be reincarnated, destined to meet again in a new life.