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There are 3 tiers to male/female character in yuri/yaoi shows respectively
>1 - family members
Everyone has a dad and a mom, or siblings or cousins, uncles, aunts, etc... These are fine unless you are very sick in the head yurifag/yaoifag or the show actually incestbaits
>2 - tertiary/background characters
Weirdly enough these tend to more dangerous to the viewer than the previous one, probably because despite being almost irrelevant, they still can "ruin the mood" for some viewers, probably because the lack of blood relation makes them a "potential partner" despite the show telling you otherwise, which is why a lot of shows tend to just not have these. They are fine as they make the world make sense but not having them is also fine even if they invite some people who take jokes too seriously.
>3 - secondary/primary characters
This is what most people have an issue with it, people watch these shows for the girls/boys, not the other gender and every time wasted on them is time it could have been used for more of what the audience wanted in the first place, at best they are a minor nuisance and at worst they can ruin a show, just dont bother with these.