Firos affection is more like that of a clingy brocon sister than that of a romantic interest,so Raphtalia should be the only one romantically involved with Naofumi, unless they put Kizuna and/or Glass onto his route,too.
For the novel, the was also that blind girl(forgot the name, it started with a I think; could be atlas, but there was some sort of shield girl,too,with a similarly sounding name,so I confounded them a lot) who was obsessed with Naofumi, but I don't think being a stalker justifies the harem tag