"The seed has fully merged with his body. Now... it's only a matter of time before the will inside it awakens. All I can do is suppress it for as long as possible."
Apparently, Sansa had already snuck into where Danzo was resting.
Using her powers, all she could manage was to keep his human side alive for as long as she could.
But when the time came, Danzo was destined to become that monster.
In that instant, I finally understood where the one-month time limit had come from.
It was her.
Sansa looked at me with quiet sadness.
Danzo had been a rare kind of friend .. even for her, someone who hadn't spoken with him much until recently.
"I think you already know... but when the time is up, we'll have no choice but to—"
"I know."
I cut her off before she could finish.
Maybe she went to see him intending to end it, but she just couldn't bring herself to kill him.
Instead, she gave him as much time as possible to live on as the Danzo we all knew.