The worst monsters were once human.

Lord Voldemort may have lost the ability to repent, but his ability to recall the past remains intact despite tireless suppression. The night of the Battle of Hogwarts, he takes a trip into the boggy marshes of memory...

Hogwarts 8th year (postwar oneshot). Padma was cursed during the Final Battle. When she finally passes away in St. Mungo's, Parvati doesn't know how to carry on living without her twin.