When two siblings love one another very much - Normalized & completely accepted - Equal freedoms

When two siblings love one another very much:

In this world, the traditional form of dating still very much exists. However, one crucial aspect of relationships, marriage, and sexual activity has been changed quite drastically. Where in our own world between siblings is usually looked down upon as gross, unnatural, taboo, and dangerous for breeding, in this world it is quite the opposite.

The only type of relationship that is viewed as normal and safe in this world, is a relationship between siblings. Any relationship or sexual activity that takes place between people who are not siblings is viewed as gross, unnatural, taboo, and dangerous for breeding.

When looking for a romantic and sexual partner to spend your life with in this world, you are expected to look towards your own siblings to find that potential partner.

Normalized & completely accepted:

All people in this world fully accept the reality of things and find it perfectly normal to flirt with, date, fuck, and eventually marry their own sibling. Family trees are simply straight lines and no one finds any problem with that. Parents encourage their kids to interact and explore one another both romantically and sexually, as if it’s entirely expected of them.

Equal freedoms:

A factor in relationships that is unchanged in this alternate world, is that both partners have equal freedoms and power within the relationship. Neither partner is in charge of the other. However, both partners are ultimately limited to dating only within their own pool of siblings. So, if you only have one sibling, that sibling is your only possible option for marriage and procreation.