Kyoko Usami is a rookie nurse who has just started working at a medical clinic on a remote island. With a population of only 30 people, she struggles to adapt to the inconveniences of isolated island life. Her life changes forever when a mysterious black lightning bolt strikes the island's shrine, shattering an ancient seal and reviving a wicked demon. Kyoko happens to be at the scene and is granted the "Power of Radiant Light" by the shrine's deity. Tasked with the mission to reseal the evil entity, Kyoko transforms into the magical heroine Twinkle Heart. Now, she must balance her duties as a nurse with her new destiny as a protector to save the island from the encroaching darkness.