In the 1st episode of the anime adaptation of the manga The Quintessential Quintuplets, I noticed there was this change. The younger sibling Raiha Uesugi of the protagonist Fuutarou Uesugi calls Fuutarou's classmate, Itsuki Nakano, as 'Itsuki-san' instead of 'Itsuki nee-chan' (and instead of Naka...