Under Persona 4, Narukami Yu and Seta Souji are the same character. In the base game there isn't a default name. Seta Souji was the name used in the manga. Narukami Yu was the name used in the anime and has been used repeatedly since. I don't know if you want to leave them as is or replace them with Persona 4 Protagonist. But since you have Persona 5 Protagonist for Persona 5 I thought I'd mention it.

Persona 3 has a similar issue with the male protagonist. The female protagonist of 3 only has a canon name in the musical, but I've never seen it used. I usually see people do a feminine version of the male protag's name.