Some suggestions for combat:
1. No need to announce the start of the next turn, just creates another screen to click through. Unless you are planning on having the ability to do things between rounds (Like flee) then I would remove that screen entirely.
2. Maybe have a dialogue check at the beginning of the fight to give you the ability to lower the enemies defense some before they realize you are a threat? Kind of like the damsel in distress angle the first person you try to do the HJ to. I know Succubi are a known quantity in this world but I think there's still room there for a pre-fight advantage.
3. Adding to that, you can choose to start combat as full succubus form (Give a slight bonus to stats) or in human form (Maybe get a couple surprise rounds). Different enemies could be more vulnerable to different forms (A knight may be vulnerable to being hit on because of his ego, but a farmer may know no 10/10 hottie is flirting with him).
4. I would look at making combat faster, with both player and enemy taking more damage. 12+ rounds is a long time for a turn based game with so little options.
5. Others have pointed out balance is wack, with level 2 enemies being easily 3 times harder to take down than level 1. I respect that early dev you are more focused on getting things down than balance. I would recommend erring on the side of "Too easy" while in development just so people can see more of the game faster and without grinding (alternatively, have a debug that gives player infinite HP and can add gold at any time).
6. Maybe absorbing essence can give a temp boost to a couple stats from the creature killed, letting players "Chain" kills. I think it fits with the lore and could be a unique premise.
I think you have a good unique premise. Others have already talked about the size and Time to Porn so I won't belabor the point but at the end of the day its your game, so do what you want. I'm looking forward to future updates.
Oh, also the first kill does kind of come out of nowhere. I think a good way of making it a little more reasonable is if the PC charms the dude, chickens out of the HJ, but the dude is so horny and out of control that he tries to force himself on the PC. Should give her an adequate reason to kill, make her still feel like a murderer, but its not just an execution.