Hey, thanks for the questions, and apologies for the late response.
There will be darker choices and scenarios, which can ultimately result in players entering the 'corruption' route of the story if enough of these dark actions were taken. For example, the next update will give the choice between showing mercy to the enemy or taking lives. I'll be adding a lot more of these good/dark choices over the course of the game, as well as some moral dilemmas where there isn't inherently a right or wrong answer. The MC and Valerie can choose to either reject or embrace their demonic temptations.
I like your idea of being able to take the elven sister as a slave. This might be a bit difficult to implement right now, since Annestria plays a major role in the story and making her an enemy would require a lot of changes. But I think this is an interesting way to take both the dark route and sexual content, and I can add it as part of my long-term plans for the game.