Usotsuki wa Imouto no Hajimari
嘘つきは妹のはじまり
A 20-year-old thief named Mikaro targets Tsubasa, a high school student who recently inherited a large estate. Believing she has entered a hidden treasure room, she discovers only girls' clothing. After being discovered, she agrees to Tsubasa's request and pretends to be his younger sister, acting like a middle school student. The story includes three additional short chapters.