Reborn as the Male Lead's Unlucky Blood Bag

[Pseudo transmigration into a book, both leads are each other's first and only, 1v1, past and present lives.]

Bai Wei transmigrates into a book one day, only to become the most pitiful supporting female character in the story: the hapless blood bank for the second male lead. Though she's rich and beautiful, she's willing to be drained dry for him, and in the end, he kills her with a single stab.

On her first day in the book, Bai Wei catches the second male lead draining her blood and kicks the scumbag in fright.

Just as Bai Wei is settling into a peaceful retirement, she accidentally triggers the "Keep the World Pure" System. It makes her stop the second male lead from meeting the female lead, indirectly saving his life in the process. But to stay alive, Bai Wei has no choice but to complete the missions.

But why have the female lead and male lead broken up? And why is she blushing and smiling sweetly at the male lead's uncle?

Why has the male lead accepted someone else's confession? Has he settled down, too?

Why does the second male lead keep acting against the script? Why is he acting all sweet with her? Confessing to her?

After an accident leaves the second male lead in the water, Bai Wei regains her memories. It turns out none of them are characters from the book.