#science!sans

The start of it is when Dream killed Nightmare, and all that was left is his apple.

there's a plot hole that nightmare's apple somehow did not got purified from dream's touch but i prefer to think that it doesnt work through gloves so please bear with me

Dream couldn't bear a thought that Nightmare isn't here, even though it was his mission to get rid of him for the sake of multiverse's safety..so he goes to Sci and begs to help him, and this is where everything starts.

The story goes on and Nightmare slowly gains sentience because of the memories tied to his soul from which he's working, and he finds out that he's not the first android to be made. Every other Nightmare-droids that get sentience and freak out that they are a machine now were destroyed and everything starts from scratch.

I like to think that Nightmare-droid is a completely different person, tied to Past!Nightmare and Corrupt!Nightmare with memories only, but in the same time the idea of Nightmare knowing who he is and understanding that he's basically trapped inside of the machine is so unhinged that i like it more.