Katia-ch
an
Make perfect sense why you didn't remember her. I'm not sure if they introduced her better in the other format(webnovel/light novel), but they introduced her here the same way they introduced the great swordman guy. Practically non-existent & than suddenly "meet them since childhood".Gotta be honest, don't remember who Fia is and why Emilia is so wary of her. I remember the rest lol.
also, doesn't bother me if a harem if the girls also love each other and get along. Just don't go over board with the amount of harem members lol.