Summary:

She was captured, drugged, and beaten.
Face to face with her own sister.
With her life on the line, the founder and leader of the Phantom Thieves, Makoto Niijima, must prove her justice and mend her relationship with Sae... by detailing the events of the past year.

A T.V tropes page is available here: https://tvtropes.org/pmwiki/pmwiki.php/FanFic/QueensCheckmate