Each game will have a big choice in it that I'll ask in the final game that might result in the True Ending.
These choices might also result in unique encounters in the next game. For example: if you side with the witch hunters, you might face a unique succubus that they were hunting and asked for your help. If you side with the witch, you might be able to deepen the bond between you two. Etc
And I might go for a trilogy for each Era, instead of 4 games.
One of these 4 games was supposed to be more about exploration than story, so what I will do is to open the world a bit more in each game, instead.
Now that I'm finishing my first game, I have a better idea on how development works. Not to mention that I have side games like Warlock Saga that I'd like to expand as well.
The story won't suffer, and the quality of each game might increase.
It's magic. They drastically increase your normal desire to insane levels.
Even weaker succubi like White Demon can convince strong men to give up. Although a normal man could refuse and attack her.
Lesser and medium clans can be fought without a magical relic, but you will need to be extremely strong willed, like Red Winter.
Meanwhile, royal succubi overload your brain completely. You will NEED magical help to resist their temptation.