Undertale & Undertale Au Roleplay Book

Dream's Incantation {Dreammare}

Dream and Nightmare knew that their destiny was always bound. Even if they did not like what would happen in the future one day. Nightmare's destiny was that he was bound to get corrupted one day by consuming a dark apple and Dream would become Nightmare's enemy. Nightmare of course, didn't know that but Dream did. However, Dream finds an old dark magic spell book one day. It contained a spell that could break a person free from what was destined to happen to them so then the person would be able to choose their own destiny. Dream didn't tell Nightmare about finding that old dark magic spell book somewhere and of course, Dream wanted to try the incantation that was needed to break Nightmare and Dream free from their assigned destiny. However, Dream just wanted Nightmare to be happy. He didn't care about his own happiness but he wanted his brother to have a happy ending. But of course, there was a cost to doing this incantation. More specifically, the cost only took effect if an element of light used this spell...it could cause the element of light to become corrupted...
But if an Dream uses this incantation to free Nightmare from the possibility of Nightmare ever getting corrupted, Dream would become the one everyone hated while Nightmare would forever be in passive form and everyone would start to actually care about Dream but what happens if one night, Nightmare figures out that Dream left their house (they don't have a castle) and that Dream had left a note saying he left to do something very important and that Dream didn't want Nightmare to follow him but what happens if Nightmare still goes out and looks for Dream and finds Dream...doing the incantation which Nightmare would recognize the incantation since he heard about it in old legends? How would Nightmare react to the fact that Dream was doing an incantation that could end up harming Dream?

//I wanna be Dream for this//