The Unfair Equivalent Exchange

When Roy Mustang regains his sight, he is forced to pay another price - even though he has the Philosopher's Stone. Now, with the help of Riza Hawkeye, the Elric brothers, and other faces brought into the conflict of the Promised Day, they must all help to regain the Flame Alchemist's memory.

Royai, Ed and Al guiding Mustang, nothing explicit or mature. There are spoilers to Fullmetal Alchemist: Brotherhood and Manga, and so if you haven't watched or read the manga or Brotherhood, or finished the story, I advise you not to read this.