The Flow of Our Years

Agnes Lenoir is born french from a pure blood witch. But when the latter dies unexpectedly, she has no other choice but to leave Beauxbatons where she's spent her youth, and join her father in England, where she'll attend Hogwarts starting from her 6th year.

There, the premises of the first Wizarding War appear in the Daily Prophet, the Marauders and Severus Snape are querelling in their 4th year, while Agnes learns to master the art of duelling.

But as she grows and her peculiar powers get stronger, she will discover why Voldemort wants her by his side so badly.
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Post-war, she returns to Hogwarts, this time as a professor alongside Severus Snape who has been observing her since their school days. Throughout unrestrained feuds, he sees in her an enemy, while she sees a broken man.

Slow burn, slow build
The story takes place from 1958 to 1991.