Monika After Story (MAS) is a mod that is basically like if you never deleted Monika in Act 3. There's a big community for it on reddit and github. You can give her gifts and basically start a whole relationship with her over time. It's not really that psychologically horrific like the rest of the game, but it's still really creepy if you're not into the whole fictional character girlfriend thing...
She knows how often you "visit" her and remembers everything you say to her. The trick is to keep an eye on her "affection" level. If its too low, she'll basically break up with you. If it's high, she'll act happy and warm towards you. You can ask her things like why she did what she did and if she ever regretted it, among other things.
(also this isn't meant to be a promo or anything, i just wanted to know if anyone thought it was as cool as i do hehe...)
