Hello! Thank you for the comment!
There is a vanilla route for this game, and there is a story to discover if you can finish it that way, but since this is an NTR-focused game, the vanilla ending might not really be a big deal, maybe some flavor text about world-building. But there's no harem end tho, since even if you are already going out with the heroine, she will still get attacked and will enter the NTR route where she is having an affair with another male if you let your guard down, so the NTR route has 2 version where she is your lover but got NTRed or purely become someone else lover before you get her.
For SPH and SPA, I'm sorry, I don't know what that means, but from a quick search, it seems like it's 'Small Penis Humiliation' and 'Appreciation'? I guess? Regarding these, both heroines will not humiliate MC at the beginning, and if they were properly protected, the trigger maybe cumulation of corruption and their relationship to your rival males. So if you decide to go the vanilla route, the heroine will even give a positive comment about it.
Unfortunately, there's no shrinking and growing mechanic of the penis for this game, since it's just to display a penis with flavor text of how the heroine currently thinks about it, but maybe in the future game? I also quite like that mechanic, but it's just not compatible with my vision for this game.