After almost 3 days I finally nailed down the skills system:
seems complex but is very similar to Spirited Heart, with the addition of the Virtues/Sins already seen in the second episode, and levels! Instead of using a simple 0 to 100 value like in my previous games, I use a 0-1000 with a level every 100 points to make it simpler. Is a bit like RPGs, where you "level up". In this game don't plan to repeat my past mistakes, so all actions increase the skills (you never get a negative or zero value change).
So there are 6 romance endings (when they offer to marry you, the game ends) and 14 virtue/sins/skills ending. There is an ending for every sin and virtue, but to reach it you also need to maximize a specific advanced skills. For example, the Chastity ending will require maximum Chastity + Level 10 in Faith. The Lust will require maximum Lust + Level 10 in Dancing. And so on.