Harmonia

Harmonia summary:

Divers discover an immortal jellyfish in the Caribbean Sea and the key to immortality is seemingly at hand for humanity with the development of Harmonia, a pill that keeps its consumers looking young as long as it is taken daily. However, a fatal flaw is discovered when a singer experiences its side effect while on TV, rapidly aging until death. Trapped on Nakwon Island with his family, islanders he's known all his life, a group of church volunteers, and a dwindling supply of Harmonia, will Junam be able to escape alive?