"Top of the World" (世界の天辺, Sekai no Teppen) is chapter 445 of the original Naruto manga.
After the death of his parents, Nagato wandered Amegakure to look for food, something that was in scarce supply due to the ongoing Second Shinobi World War. When he was about to die of starvation he was found by fellow war orphans Konan and Yahiko. They saved him and became a sort of family, but they could not escape the terrible realities of the war. Upset by the constant deaths, Yahiko vowed to someday rule the world to establish peace, a philosophy Nagato also adopted.