Femdom Free Use/Rules
Background
The world of Femdom Free Use is like ours, modern, with regular jobs and schools, but with the exception that all girls are legally allowed and encouraged to have sex whenever and wherever they wish.
There are no public lewdness laws. Having sex on the bus or in class is not seen as any different than having it in your bedroom. In fact, it would be a weird day indeed if you went to work and there were only one or two people having sex openly.
There are no public indecency laws. While most people wear what we imagine is typical clothing, this is by no means mandatory. Girls, as the dominant gender, may of course wear whatever they wish, including going naked. Fashion magazines have various topless or bottomless styles, or girls may choose to go bottomless or pantiless for practical reasons (easy to have sex). Boys, as the submissive gender, can be stripped however a girl sees fit. Many will go bottomless for convenience reasons too, as it is much less of a bother if a girl wants to violate him if he doesn't have to pull any clothing down. Dress codes, where they exist, tend to only target men.
Sex and nudity are considered very casual and normal. Social media sites like YouTube do not have "adult" filtering, and treat hardcore sex no different than videos of puppies playing. Advertisements frequently show girls violating or dominating men, and products targeted towards a male demographic are framed in terms of their social expectation to please women. Sexual products like toys are sold like other supplies, no different from pencils or vegetables.
There are no age of consent laws, and no stigma at all against underage sex. While it's not illegal to go younger, generally people only have sex with those who are 10+. It's very common for sex to be both close-in-age and involve huge age gaps: a cougar fucking her son and her little friends or a middle school girl sucking off her adult male teacher are both common things to see going about your day.
There is no stigma against incest. Girls can use their fathers and brothers just like nay other boy. This doesn't mean some girls (and boys) don't still have a fetish for it! A child not ever having sex with their siblings or parents is a very unusual case.
There are no rules against "blue-balling" the people you use, but it's considered rude if a girl does not at least offer to get her partner off after she has orgasmed. Chastity devices are illegal for all genders because they limit the inalienable female right to sex. Condoms and similar items exist, but are used extremely rarely.
Girls have full conscious control of their pregnancy. Normally, girls are having sex for pleasure and so choose to be infertile. However desiring a child even as a single mother is very normal for teenage or older girls, and with many social support programs, it is not at all an unusual arrangement. Girls can choose to become fertile during sex, selecting the sperm they think is the highest quality. Boys have no say in whether their partners become pregnant, and have no parental rights unless the mother grants them.
Semen
Cum is a given special cultural significance. It is a sign of female domination over males. Advertisements show women with facials, or with cum staining their clothes, and "cleaning up" after sex is considered a weak, masculine thing to do. For a boy covered in cum, it is a sign of his defeat, of his weakness against female flesh which is free to violate him whenever it wishes. After sex, girls will either leave the cum there, such as allowing a creampie to drip out, or will force a boy to lick it up.
However semen is also considered a tasty treat. Girls will suck off a boy just to see how it tastes, and a child with delicious spunk will soon be used to a lifetime of every girl imaginable using him as a simple semen dispenser. Taking supplements to boost cum production is common. Here, girls "cleaning up" is not considered weak or un-womanly, but in fact a justified response to make sure she gets all the cum she wishes to sample. (Yet curiously, a boy eating out the same cum would be considered submissive for it.)
Gender
The most common pairing is obviously girl (or group of girls) x boy. However, the law does not explicitly say only boys are permitted to be used: girls are free to use any other girls as well! This is less common due to the matriarchal culture which privileges women over men, but it is definitely still prevalent. Almost every girl is bisexual, and because girls are raised to be so horny, love groping and sucking their friends just like the random boys they find.
Trans girls are in an interesting position. As girls, they have the same sexual rights as cis girls, and can freely use any boy (or girl) as they wish. However, for as long as they have a penis, they are frequent targets of other girls wanting to get off. Like males, they have no say in pregnancy or parental rights. Even when taking hormones, trans girls do not become sterile, and are every bit as fertile as cis boys.
Trans girls tend to be proud of their penises, and how they have overcome the weak masculine side of their nature to become dominant and feminine. Violating men's butts or mouths with their girl cocks is a fun sexual pastime. Due to different hormonal effects, girls typically have larger penises than boys.
For trans girls, cultural ideas about the dominance and submissiveness of semen are reversed.
Consent
Technically, there are no laws against rape. Not getting consent is not considered a serious offense, given girls have an inalienable right to have sex whenever they wish, and boys are perpetual cum dispensers. The case of a male raping a female is unheard of, as no boy would ever dare to do such a thing, and the girl would probably enjoy it so much it would be more her raping him. Among friends, friendly gropes, sucks, or even casual penetration is common and not a big deal.
However rape cannot be violent. If it's an unwanted blowjob, then people will perceive it as no more severe than jaywalking. But injuries, whipping, and other forms of harm is illegal if non-consensual and prosecuted under mundane assault laws. Girls only have a right to sex in as much as it does not infringe on others. (However, offenses against men are generally not prosecuted as harms to them, but rather as inconveniences to other women, even hypothetical ones, whose right to have sex is being affected. Remember, this is a very matriarchal society.)
Guidelines
While this is "femdom" free use, keep things largely gentle. If you add BDSM elements to your story, please tag it so others know. The "femdom" here is mostly about girls being sexually in charge, and males considered as the "naturally submissive" gender.
You can write boys as assertive and girls as shy, but remember the main aspect is girls using boys. Even the most "chad" male will submissively obey as a shy girl uses him as a masturbation toy, it's just the natural order of things.
The boys should not be in pain. At worst they should be bored, inconvenienced by yet another horny girl, or interrupted by an unsolicited orgasm. Of course, they can also enjoy sex, but do so at the whim of women.
Girls should be very horny. Imagine the various stereotypes and expectations applied to men in our world, they're lecherous bastards, they never say no to sex, etc., and apply them to women instead, and that society thinks they're divine qualities.
Have fun! Imagine what a world would be like with such altered gender roles and so much open sex. There are a lot of fun things to write about!