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.

[Slytherin][Hermione is the only female protagonist][More rigorous: After living in another world for ten years, the protagonist barely remembers a little about Harry Potter][Not a system]

The false devil:

Gather the Saints to fight against the Muggles.

Occupy Britain and attack the school.

The real devil:

Destroy the world and cause great suffering to all living beings.

Elias traveled through time for eleven years and suddenly found out that he had traveled to the world of Harry Potter and was chosen by the bloodline of the devil!

You only need to gather three of the seven deadly sins: pride, wrath, laziness, greed, envy, gluttony, and ecstasy, and the power of the devil in your blood will automatically summon the devil to possess you and destroy the world!

For the peace of the world,

From that day on, Elias knew that his idle life would be gone forever...