Love is Magic: Ms. Magician with a Male Phobia

Kaori receives a strange job request from a female magician who requests that her protector be a woman herself. Ryo sees that this is due to her having a phobia of men in general. As a result, Ryo resorts to cross dressing as Kaori's older sister in order to protect her from a rival magician seeking to push her out of business.

Synopsis excerpt via Kitsu.