Maybe it's to atone for his sins?
Maybe it's for revenge.
Severus decided to continue being the villain, serving as the double agent between Dumbledore and Voldemort.
To gain Voldemort's trust, Severus was even willing to shoulder everything, killing the great Dumbledore, allowing himself to be misunderstood by everyone.
But before seeing the final ending, who would have guessed:
This was something Dumbledore had actually asked Severus to do?
Before this.
They had once had a fierce argument over this decision.
"I beg you..."
Dumbledore's final request before his death wasn't begging Severus for mercy.
On the contrary.
Dumbledore needed Severus to kill him, thereby earning Voldemort's complete trust.
Their argument had to come to an end.
Of course.
Dumbledore had another reason:
Malfoy could still be saved—he couldn't let this child's hands be stained with his blood.
It was as if Dumbledore had forced Severus to act.
