I sort of just had this idea in my head of what if Grim Sonic was in Friday Night Funkin'? I would think that he isn't hired by anyone, or is someone who wishes them harm or doesn't want Boyfriend and Girlfriend to be together, but the real reason why he would go after Boyfriend and Girlfriend is that they are always getting themselves into these dangerous situations, life-threatening experiences, meeting dangerous people, and because they're stupid, they're fearless. So, he comes in to bring them the fear of Death and to teach them a lesson to not mess with the fire that they lit. And to take their souls because he believes that they don't value their lives anymore because of their track record.