[Kurona]

I think really it just helps if you know a little something more about the character to make them feel a bit more real; just something that makes them much more of a person, and an outside hobby or job can do that. Looking at examples throughout Rider you've got Hina Izumi from OOO being an aspiring fashion designer; Akari Tsukimura of Ghost's cast being a scientist in the making; Mari Sonoda from 555 wanting to be a hairdresser. These traits allow these characters, at least in my opinion; to stand out a little more among other heroines in the franchise because they have their own goals and interests outside what they meant to the main character.
(this isn't to say they're the only ones or even the best ones -- heck, my personal favourite heroine in Rider is and probably always will be Agito's Sumiko Ozawa. Just some good examples I could think of that fit the bill here!)

So here for instance, it might have benefited Nozomi if say... maybe she said her favourite subject was History; or she mentioned she was in an Astrology club; or maybe there could be one of those trope-y scenes Toku oh-so-loves where she reminds Mutsuki that they had promised each other they'd help reach their dreams or yadda yadda. Nothing much, just that dropping small details into a throwaway line or two would help make her feel more real!

As-is though, she does still fill her intended purpose quite well; and as said it's acted quite well too! It's just nice when these characters can feel more like people than plot devices too.