It's in the age of exploration, the maps have not yet been filled out and many brave adventurers set out to see the world.
A large family of 16 ends up stranded on an otherwise uninhabited island that has been undiscovered til then.
They consist of the 25 year old mother, 24 year old father, seven sons aged 13, 11, 9, 7, 5, 3, and 1, and seven daughters aged 12, 10, 8, 6, 4, 2, and 0. A large family owing to the religious convictions of the parents that God wants them to produce as many children as they could.
As the player (and voice of God) you will guide the family and tame the island with them, at first it seems the ultimate goal is escaping it and making your way back to civilization.
However, in the meantime you will be able to make any of the family members engage in sexual congress with one another, tough this is just a part of managing their interactions and relationships to one another, there'd be a lot of social dynamics that could form between the family members, incuding those awkward interactions from relatives who are aso fucking.
The main focus is on using the family to conquer the island, build a camp and upgrade it, gather resources and carefully oversee their use, fight against the beasts who threaten your clan, survive natural disasters or outbreaks of illness, and more.
You will follow the family over the time when they inhabit the island, they will grow older and some may even die of one cause or another, there are multiple paths to victory and some are reached by using your family to create a new civilization on the island.
Since these are family members you must manage the issues that come with inbreeding and overcome obstacles like the natural psychological aversions to having carnal relations with close relatives, but achieving these feats are very possible.
A harder mode is available where you can manage different familial arrangements, having less clan members naturally means a more difficult game, the lowest you could go is starting with a pregnant mother who would give birth to a son, and together those two must escape the island or populate it.