[Spoiler I guess if you haven’t watched the ending?? Which I’m assuming everyone has…]
When Shiro reveals his identity as Adolf K. Weissman, he also confirms that he is still Isana Yashiro. This always confused me a bit because I wondered who ‘Isana Yashiro’ was before his body was taken over by the Colourless King, and then by the Silver King. But ‘Isana Yashiro’ didn’t exist before Weissman’s soul took over, because it’s a made up name!!
Neko made up his name, along with all his memories of his identity, when she found him in the storage room after he fell from the sky. His name was fabricated based on a poster of Isana Shrine on the back wall of the storage room. The kanji for ‘shrine’ （社）is the same kanji used for ‘Yashiro’. This poster also shows up on the TV screen in the train station, as well as on a calendar in Shiro’s dorm room.
Anyway just in case no one noticed this before… yeah.