Lesbian tag. If it's a male protagonist harem game with the lesbian tag, it's a safe bet that it has the "bi LI trope" because why else would there be lesbian content in a harem game? Not sure why the harem tag is missing though, that seems a silly oversight on the dev's part. MC is railing the whole cast with zero conflict between anyone, and trying to make a non-harem game out of this storyline so far would just be silly.
Not necessarily something the dev left off. Even if a dev has control over the thread for their game, staff, moderators, and uploaders all can update the tags. If there are tags missing, you can request their addition by clicking
Report on the OP (like you see on my post here in the bottom left). Choose "Other" for the reason in the form that comes up, and then in the text box, indicate any tag(s) you feel a game should have, with an explanation of why. (Obviously, here you could just say something like "The MC is having sex with many women, and most — all? — of them know about it and are fine with it" or something similar.)