Kuroyuki Hime: Snow Black

Raised from commoner to princess by a king who saw her beauty and wanted an heir by arrangement, the protagonist—nicknamed Snow White—had accepted the terms. The prime minister Reviens Tendre could not: consumed by that same beauty, he murdered the entire royal family, dressed himself as the "queen," and took the throne. The protagonist, the only survivor, escaped into a forest and found the Alliance of Seven, who share her grievance against the new ruler. But the "queen" is half-mad since she escaped, and love and obsession are moving toward each other in a way that has no clear ending.