Back to the days when Rughelia and Silk were kittens, and Mocho had lots to do! 
Rughelia was adopted from a Forest family, as I said here: https://www.furaffinity.net/view/44213856/
while Silk is the natural daughter of Mocho, and a wildcat in the same tribe where Rughelia's parents live. They grew up like sisters, this mean fighting like hell every moment until they got slapped by the big paws of poor Mocho. But they also love each other a whole lot.

The birth of a spirit is quite the rare occurrence, as they usually die and reincarnate in a body that can be of different ages and phisical shapes, but contains the same spirit of the old one. So birthrate in the Big City and the Forest are low, but having not a pope of some kind breathing on their neck, they're not very worried about this. The generation of a spirit usually comes from two spirits being in a very high state of connection, but it's not the only way they are born. They can be born from a single other spirit, from multiple ones, from spirits and other creatures, and even from nothing, though these cases are not very common. Also, you don't even need gonads most part of the times to make a spirit-baby. Not if you don't want to. 
Sex it's mostly just recreational so have fun.

The Iron Tree Tribe lives in an old building, where the generator that gives energy to the whole City resides, and they are its guardians. Almost all the residents are females, the males living in sparse smaller groups. Their Matriarch is Beausoleil, also known as Fluffy, that is the mother of many of them, being very, very, very ancient. She's the one with just one limb left, you can't go wrong. Hi, grand-grand-grand [..] grandma!