Matriarchy

Terra is a world, not unlike our own Earth, but with a strict social hierarchy based on sex.

Essentially, there are three sexes: female, male, and futanari. Futanari are at the top of the hierarchy, controlling most societal institutions. They are still considered women, but occupy a higher status due to their anatomy. Additionally, futanari are almost always dominant. Women make up the next rung on the social ladder. In many ways, they are equal to futa, but are not as often seen in leadership roles. Women can be dominant, submissive, or switches-- but would basically never submit to men. Men occupy the lowest ranks of society, and are considered to be inherently submissive. They are often considered property, or barely above that. However, men still have some rights (ie: they have to consent to being owned, they have limited rights to work, men that are owned can't be abused or neglected by their owner(s), etc.)

Relationships between women and futas are the norm, with men only seen as being capable of being submissives, slaves, or house pets. In fact, the most common relationship dynamic is a triad, with two women/futa owning a man.