I don’t think the chapters are even long enough to accommodate more than the two leads on a regular basis, anyway. Plus, they’ve made next to no progress with one another, in any case, so the introduction of a third character could be disastrous at this stage.

I’m thinking she’s going to be a sort of combination in-universe shipper and jealousy catalyst. She already recognizes that there’s something between the protagonists, and has an interest in cheering them on, for research for her manga. (And as an aside, that was a good example of overdoing “localization.” “Adult comic” and “adult comic artist” are awkward and clunky phrases, and most manga readers would’ve understood “eromanga” and “eromangaka.”) But she’s also impatient, impetuous and apparently, judging by the surprisingly NSFW last page, a bit of a horndog, so she seems likely to get involved herself, and potentially trigger some jealousy from Renge (much, I’m sure, to Renge’s surprise).

And yeah - it’s funny that her temporary side gig, while she works toward her goal of becoming an eromangaka, is as a surgeon.