Ey bro did u remember how to get the girl beside Melanie? I'm trying to import my save data to my pc but failed and ended up with my gallery can't be unlocked T~ T
But i do completed it and forget bout this one girl T~T
I found it. You have to go to Annie's octopus level, and while there, you have to call Rose several times until she says she's tired of you calling her repeatedly. Then you go to where the succubus that appears when you break the red crystal is, talk to her and go up to the surface, you have to talk to Mason and the NPCs that are up there too. Then you go back to the beginning and talk to Rose and ask her to call Melanie. And that's it, you can now return to the surface where Mason was alone and should be with Melanie. That's the animation.