I think a fairly decent recommendation would be Leane of legitimate crown, it kind of covers many of your points and... it's a complete game.
Basically we are a male general, there is a civil war that serves as prologue 2.0 then we get to the main point of the game in which we fight an enemy nation that if they capture your female generals will rape them and make them fight for them or the king bastard will be trying to get the female generals into his harem.
So going in order:
-It has a strategy level gameplay. It can be fun to play, while it's strategy level it's mostly our character using skills or attacks against other characters so it's kinda "RPG" too.
-There is a map and you move around in it to conquer other places or to visit villages to buy stuff.
-There is an actual plot for the game and don't want to spoil it.
-We have a MC that can see the girls falling into depravaty by being raped by the enemy or having sex in the harem, the girls do have comments related to how much sex they had, even more 4 girls have bad endings depending on how much sex they had with other men.
-Tags out of those:
*Pregnancy: Girls can get pregnant in the harem by the king or by enemies, if they are by enemies they will showcast it and kinda taunt you (it isn't bad ending style)
*Rape is in the game, all the girls will resist at first when forced by their captors, however by the end of it you will have multiple archetypes (some will fall in love with the rapist enemy, others will only obey in fear or forced, while a few will fully comply waiting for a chance to go back to your army).
*NTR is kinda core in the game, most of the scenes are of that nature, to my liking too much NTR, would have liked more rewards for our MC.
*Slavery is exactly what the enemy does with your female generals if captured.
*Some of the girls are blackmailed by the enemy to continue to obey them.
*Romance is in the game, the king won't ask for any girl that you have romanced to be put in the harem. You can only romance 1 girl per playthrough thought.
-There are some records of with whom the girl had sex with, be it the hero, the king, enemy generals or random characters.
-Be it in the harem or when they are getting raped by the enemies the girl sprites will have less and less clothes.
-Illustrations are kinda good.
Overall being corrupted has some effects on the girls (being raped by enemies will lock the girl route, when you talk to them they will be sex focused and stuff like that) but you can always recruit again all girls that fall to the enemy (but they may refuse for months before they accept) or that are in the harem to keep fighting (some may ask that you don't take them out of the harem cause they enjoy it there after being corrupted enough).
Bad points in the game:
-It's very easy when you know what you are doing.
-The AI is really bad, I could play it around in the hardest difficulty to not even attack me, even more they have an odd bug related to not recognizing a place to attack it when it has prisoners.
-The enemy only has one place to attack from and it's easily defended, you can open more routes for the enemy to attack but... the AI is kinda bad, really bad.
-Some people that don't know some basic information will get 1 forced NTR scene with 2 girls of the cast. Basically you need to have the main girl (the one that appears on the last events before conquering the main city of the first part) at 100 loyalty to be able to prevent NTR.
Improvements that I believe the game needed:
-Move captured heroines deeper into enemy territory as time passes (some of them have events to instantly appear deep into the enemy territory but that's really meh and they are easy to rescue before then).
-Strategies towards heroines (taunting a heroine into attacking without orders, sending kidnapper units as spies trying to kidnap a heroine, blackmailing or using an already captured heroine to bait another one into giving up...)
-More ways to attack, enemy feeling stronger the more territory it has (basically there are 2 hidden ways that the player can open into your territory, I would have liked more enemies that would do "expeditions" through them to give me a bit of a challenge and that the more territory they conquer and the longer they have it, the bigger number of units they will have).
-More rewards for the MC (most of the girls have just 1 sex scene with our MC, I was kinda disappointed that he was rewarded so little, at the very least having 5 or 6 scenes each would have been great)
-AI rework (it would be kind of easy to program a 3 way attack, like accumulate troops on certain places then the attack expedition starts, the AI kind of does it on a 1 way attack, which is more than disappointing even more when I can even manage to nullify their will to attack because of AI fails).
-Garrisons: Having all territories be able to have a militia or some kind of defense force that help protect the territory.
-Traps: The enemy being able to block a road and preparing a decent attack to try to capture a heroine when you send her to conquer, making you feel the need to rescue her.
-Impossibility to recover troops on territories cultured by the enemy: Why would you be able to recruit on territories that were already fully under the enemy? you would need some time to actually be able to start to recruit in that place.
-Too far gone point: A point after which the girl is fully lost to the enemy/harem, while the girl will be affected on past experiences when you talk to her I think that there should be a point in which she fully falls.
-Chance of escape when defeated: That when you defeat an enemy general or a fallen general from your army there is a chance to escape based on multiple factors (loyalty towards the enemy, personal abilities, level of the character...)
-Removal of the harem system: I get the concept but I think it ends up more annoying than anything else, basically the king wants concubines and moves around the map always going in the direction of the heroines, if he doesnt have enough concubines he will send his royal guards to get them for him and force them into the harem, royal guards are very hard to evade.
On another point the harem system is incredibly easy to nullify too so I guess there is that. I would have liked more that they focused on the enemies and perhaps some friendly characters with not so friendly objectives (autonomous male characters that would fight for the kingdom but that they tried to seduce certain female generals, if they stay enough time with their female objective they will seduce her and they will try to stay near her) that you could permanently defeat on certain ways.
More or less with these improvements I believe the game would have been a really challenging and interesting game, especially on higher difficulties, but as it is while I can recommend it cause it is fairly fun but it isn't a perfect game. BTW don't download f95zone version, it's an old one and it doesn't have the "cheats", while I call them cheats the most useful one is just to accelerate time so the game goes faster and another one to take battle effects off to make combats be faster.
