For me, it's the feeling of complete domination/ownership and submission of your partner. She has allowed you the chance to change her life for many months, including near immobilization for the final trimester and then she undergoes a severely painful medical procedure to raise this pregnancy for 18 years potentially and it changes her body, adds breast size and leaves a permanent mark on her that a slave tattoo nor collar can hope to achieve without some serious magic involved. It's also more realistic than a Succubus crest/Slave tattoo in doing what they do. It's also a very WHOLESOME
BDSM act in my opinion, often done as a reward for a character's standing towards the individual involved, but in some cases, it can be a
very very very hard and crushing reality given to a character much like a trauma victim considers carrying the child of someone forced onto them. I am not a fan of rape pregnancies, but I do like the wholesome kind a ton. The kind that is a character thanking me for caring about her. The Usanna pregnancy in Love and Corruption is a beautiful example of this.
To me, there is nothing more rewarding in a game than this concept. Few games achieve this and typically pregnancy is a side tag, never a focus or goal. Miel/Norn games are infamous for being about pregnancy but not actually providing enough stick to make the carrot inviting.
So there you go. You have the tag. I have been following for ages, havent tried it out but I am in the middle of a crunch period. I'll get to this soon, but I hope this helped you. And
Succubus Hunter there you go. happy? lol