The Answer (答, Kotae) is chapter 444 of the Naruto manga.
Naruto meets Nagato, who makes one last attempt to capture him, but in his emaciated form he cannot overpower Naruto. Naruto says that although he couldn't forgive Nagato for his crimes, he wished to talk with him before deciding how to proceed. Since they were both students of Jiraiya, Naruto asks how Nagato could so completely abandon Jiraiya's philosophies about peace. Interested in seeing how Naruto's views differ from his own, Nagato explains how Konoha ninja killed his defenceless parents when he was a child. Overcome with grief, Nagato awakened his Rinnegan to avenge them.