I don't know if there is a full walktrough somewhere, but if you describe what problem do you encounter, maybe I could help.
First, there are 3 levels of difficulty. For first time users, I would recommend "Secretary".
Then, there are (AFAIK) two main modes of playing: pure and slut.
For "pure" play style, you would want to focus on developing your combats stats, while maintaining Karin's desires under control. I would recommend focusing on developing the blue and yellow attack types, that is, trying to use only these attack types most of the time. Especially the blue one can become overpowered with edicts, which guarantees that you always attack first and that your evasion rate is trough the roof (in the later game). As long as you focus to keep desires under control, that is preventing both the cap and the minimum desire to rise, that you can easily get the pure ending, which comes with a hefty boost for NewGame+.
For "slut" play style, well, you gotta lose strategically. Once a certain act is done to Karyin enough times, she will learn to use that as an attack, which opens a second way to win a battle: fuck the enemies until they are exhausted. For this play style you would need to focus on edicts that gives you a boost by using a lewd attack (energy is the main resource here).
This is very-very bare-bone.