I swear they just made √A because they hated the Ghouls so much they wanted to flesh out all the more likeable human characters
who werent't much more likeable than the Ghouls
Holly had to change her name to Seiko not because it was a nickname but because back when this manga came out the only way to gain Japanese citezenship was to change your name to a Japanese name
also the Japanese word for Holly is Hiiragi not Seiko