Nihon and Nippon both means Japan.
Nihon and Nippon are both Japanese ways of pronunciations to read Chinese letters indicate Japan.
I consider that the sound of "Japan" for Nihon derived from Chinese way of reading of Nihon. In Chinese they pronounce Zuban. In ancient world, Nihon changed to Japan on the long way to English speaking world.
Nihon and Nippon are both meaning JAPAN.
Japan in Japanese
I live in Nihon