He was at Hogwarts, and had just become a Half-Blood Prince.

[Parent-generation; multiple female protagonists; no system]

…

In 1976, 16-year-old Severus Snape welcomed a new life.

That year, Voldemort had not yet split his soul into seven pieces.

That year, Nagini was still hiding in the forests of Albania.

That year, Pandora was still doing wonderful experiments at Hogwarts.

That year, Ms. Rosmerta was in her prime and very graceful.

That year, Snape decided to experience this wonderful world.

If Dumbledore had not defeated Grindelwald.

If the war between wizards and Muggles really broke out.

If the finger witch that the faded one failed to meet was reborn in the body of an 11-year-old wizard girl.

My name is Hermione Granger, and I will rebuild the magic circle of this broken world.

(Contains secondary settings, rational discussion)