There are a few 'Magical Girl' games, being MahouMUSH and BattleFantasia, but yeah a lot of the problem is the split in the fan base if you go 'without FCs' or with, bot the games I listed allow FCs from various series, but also allow OC Themes.
If I were to create a Sailor Moon game It would personally have:
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No FCs ( as PCs) - Its set post Stars, and the Senshi are working to ressurecting other forms of magical girls to spread the work load - allowing for OC Themes.
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The FCs are around and a ( also the Shitenou live, they got reincarted at the end of Seasons 1 so they need to wake up be awesome male Knights...( Ala Sailor Moon Crystal).
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Rise of Crystal Tokyo- There are some kerfuffles with the timeline ( via Usagi meetin Neo Queen Serenity) (NSQ), so Crystal Tokyo's + the magical girls efforts are beginning to have an effect (magic tech, and improved life spans yadda yadda).
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The Bad Guys: Other Magical Girls- or rather 'Corruption' remember that 'Dark Sailor Mercury Arc from PGSM, its sort of like that. But there also literal Bad guys, entities and their generals (also with Magical people who've done heal-face turns-)