That makes two of us. You have little room for errors, especially in 2-1 or 2-2 and basicly have to pray she doesn't use magical attacks too much.
Nah, it's actually super easy. If you're going for a lewd ending, you can just knock her out of the sky after using the bottom left skill and immediately end the round. It helps to know what each skill does. Even if you're going for a "virtuous" ending, it's pretty easy, since once you've knocked her out of the sky you can just spam the special bar consuming melee attack and nuke her down.
Edit: Since no one seems to have done so thus far, I guess I'll explain the game systems
Your four main stats are melee attack, gun attack, defense, and speed. Melee only is relevant when she's on the ground, while gun attack is only relevant when she's in the air. While upgrading gun attack might seem to do very little damagewise, it greatly increases the rate at which you deplete her magic bar, which forces her to the ground.
It seems that instead of upgrading your skill damage, you instead use your upgrades to get ammo for them. The first one removes clothing, but only when it's the shot that depletes her magic bar. The second one greatly decreases her magic bar but does low damage. The third one is a tranquilizer, which forces her to sleep after she depletes her magic bar. You don't need this to be the finishing shot, but it might go away if her magic bar fully refills. The fourth one is an aphrodisiac, which will cause her first move after landing to be her trying to fuck you. Hitting her with multiple shots changes the scene you see. Like the tranquilizer, this does not need to be the final hit, but I think it goes away if her magic bar refills.