Mana Aida, the energetic student council president at her middle school, gains the power to become Cure Heart when Marie Ange, the princess of the Trump Kingdom, flees to Earth after invaders called Jikochuu corrupt her homeland's hearts into monsters. Joined by classmates Rikka Hishikawa and Alice Yotsuba, who become Cure Diamond and Cure Rosetta, Mana searches for a way to protect Marie Ange and reclaim the Trump Kingdom. Her catchphrase 'kyun kyun' describes the warm chest-tightening feeling of love that powers her transformation.