Looking for a Naruto Fanfic I Can't Remember the Title Of

Looking for a Naruto fanfic. I can’t remember the title and can’t find it. The protagonist is reborn as Black Zetsu’s younger brother, and Black Zetsu is a doting older brother. Set during the First Hokage’s era, the two join Konoha, teach at the Ninja Academy, and work together to transform the village.