Still don't know where special 2 is, my greatest fear is that since special 1 was related to combat, then special 2 could be too. I tried beating Ceruli alone on her starting screen but that didn't do it, haven't tried beating her in one of the screens with the harpies (and not looking forward to trying it). I tried doing a "solo" run but it is impossible, if you don't have any party members then even if you go the correct route to escape the maze you get sent back to the cave so you have to at least recruit Mirah. I'm really not looking forward to doing it but maybe super 2 could also be unlocked by reaching a certain level or beating a certain number of enemies in a normal playthrough.
Also worth mentioning that in reality I feel the game has 3 main routes, all related to what's your relationship with Mirah:
Hostile with Mirah - Don't rescue Mirah from the cabbits (she breaks out on her own if you are doing Lulu's route with Vexa or if you skip the cave by just doing the maze)
Friends with Mirah - Rescue Mirah from the cabbits while having Foxette as a companion (must not have recruited Vexa to rescue Mirah instead of doing Lulu's route)
Intimate with Mirah - Rescue Mirah from the cabbits while having no companions (must have lost Foxette before this point)
Hostile with Mirah you do both Mirah fights, friends with Mirah you only do the final one, intimate with Mirah you skip both her fights (instead of the final one you get a short of animation of an implied handjob Reki gives to Mirah and also a different ending).
Also I find it kinda weird that Ceruli's ending is the only one I found so far with explicit sexual content, also worth mentioning that Ceruli's ending gets an extra bit at the end if you recruit her but beat the final boss with Foxette.
I need to experiment some more for all fringe cases to see if there aren't any secrets, but here's my understanding of companion compatibility in a route:
Foxette: always recruitable
Vexa: Requires Foxette. Forces hostile with Mirah route (and so excludes Mirah as a companion)
Lulu: Requires Vexa and hostile with Mirah route.
Ceruli: Requires that Foxette be your companion during her fight (not sure if that's decided by who you had last or who you talked with in camp). Also implicitly requires hostile with Mirah route since otherwise Mirah is your companion in the fight against Ceruli.
Mirah: Requires either friends with Mirah or Intimate with Mirah routes. The first one only requires that Vexa wasn't recruited while the later requires that Foxette wasn't recruited.
Once again, I haven't exhausted all possibilities yet, but here's also the random ero cg you can find during playthroughs that aren't related to losing:
Foxette x Vexa - happens when you successfully recruit Vexa
Mirah x Lulu - happens in a hostile to Mirah playthrough if you don't skip the cave
Reki x Mirah x Ceruli - happens when you defeat Ceruli in either friends with Mirah or intimate with Mirah routes
Reki x Mirah (only implied, naughty bits are offscreen) - happens in place of the final battle in the intimate with Mirah route
Also worth mentioning each Mirah fight has a different loss CG.