By Day A Lady, By Night A Hunter – Episode 31

Vivian, an heiress, plays the perfect lady by day but hunts monsters at night as the wanted vigilante "Princess Syndrome". She crushes on Chief Commissioner Sebastian and forces a cohabitation engagement using her family's creditor leverage. He hunts her, then falls for her. His parents and federal elites run human experiments and plan to kill her family. So Sebastian fakes exiling her family and bears the danger alone. Vivian learns the truth and joins him, they destroy the doomsday monster. She becomes the federal hero, he proposes, and they wed happily. She remembers her past life: she was a proper lady, but he died for her. So this time, she chooses to be bold and save him.