While Valdana ended up sharing some themes with PB series, my previous attempts at making a sequel for Isis were vastly different games
-First one, which was foreshadowed in Isis' Alliance Ending, involved Isis MC (helped by corrupted Serena) brainwashing Alliance leadership during peace negotiations. Not only the cast was suppsoed to be smaller (3-4 girls max), but I also planned a completely different structure instead of Isis/Valdana rhythm of stage1-stage2-stage3-next girl plz. I ended up abandoning it very early because I could not come up with decent story to fill the gaps between corruption.
-Second one involved a corruption of an elite all-female miltary unit during a heated battle on a remote planet. Unlike Isis/Valdana, the MC was on the good side and a female, and corruptor was a villain. It even was supposed to have some gameplay. I scrapped it around 20-30% of work for variety of reasons, but mainly because I found corruption aspects unsatisfactory. Some elements carried through to Valdana though, like the character of Yoona.
So who knows what future might bring. I actually have an idea for a third game, and it's vastly different than Valdana - but it's still in larval phase and might end up in the trash bin like most of my ideas.