Pasciel special program unlocks another sequence of events with Roland that with the latest version unlock (or probably force based on willpower check) a new bad end
The Roland bad end only triggers when you lose to him during the reverse summoning ritual quest, and only if you fail a willpower check. I don't think you even need to have interacted with his corruption chain to trigger the ending, but I don't really have a save in a convenient state to test if that's the case.
1) How much times on Normal Difficulty minimum times we should to use Star Knightess Power (+4 corruption*) ?
It is possible to beat the game without using Star Knightess Power by myself at all?
There's a cutscene that leads into a fight during the festival of greed, so you can't technically beat the game without using remove collar, but you never have to manually trigger it in battle. I believe there's even a steam achievement for clearing the game without doing so. You can avoid softlocking yourself by converting stats to perkia. You really shouldn't need to use remove collar that often in the festival though.
As for how often you should use remove collar, if you're playing on normal then you'll mostly want to avoid removing collar except for boss fights you can't manage. If your goal is just clearing the game then there's a lot of leeway for corruption, but some of the later mental changes make the game significantly harder to beat. I believe there's between 200 and 300 corruption worth of mental changes, but it's been a while and the number varies depending on what you do during a playthrough, so don't focus too much on that estimate.
