A third-year bespectacled girl who dresses as a witch and runs a little sister cafe called "Lyrical Sisters."
She was abandoned when she was one or two years old and was adopted by a university professor because of her mathematical intellect. The cosplay café belonged to her adopted mother, but she soon past away because of illness. She lived with her father in Massachusetts after that, but returned after earning enough money and bought back the cosplay café.
It's revealed that she knows Shougo's real sister and does not want her to be exposed to Mikadono family because she is an illegitimate child. But after Shougo made a promise to protect her, Mei said she will tell him if he proves himself that he's a good older brother.
