Mandatory Monthlies for らんま

[Spokavriel]

Are there any fics out there where Ranma is unavoidably female for 1 week every 28 or so days because of female biological necessities?

I know there are a couple fics where Ranma finds she can't turn back because of it but I don't remember any fic where Ranma has a regular monthly cycle ensuring she doesn't miss her time.

[Shanami]

Brother's United by genhoss is a Ranma/HP cross that definitely includes that.

The Wild Horse Thesis by Calamity-Queen of Cordite is a R/NGE cross that does it as well.

I remember a few others where it definitely occurs at least once but the regularity isn't mentioned. If you'd like, I can post some of those as well.

[Spokavriel]

Its the regularity that I am really looking for. I've read both of those as well as a couple Harry Potter crosses that have the can't change back. Just no sign of anyone taking on a cross where they keep track of time and have the regularity in there.

[Shanami]

I think one of the issues you're going to run across in that search is that very few fics have the appropriate timescale to deal with that. I'd like to see it too, but most either don't span months, or if they do, they won't touch on the period every time it happens. In fact, I think The Wild Horse Thesis is the only one I know where it gets mentioned twice even.