Syrusly?

Syrus is a Sans and Papyrus fusion.

No, this is not a fontcest thing. Don't make it weird.

Basically, Papyrus was badly injured while sparring with Greatest Dog and was slowly getting worse.

When his body turned to dust, Sans quickly absorbed his soul as to keep it alive but accidentally absorbed it.

Now for one SANS AND PAPYRUS CANNOT READ EACH OTHERS THOUGHTS. They may house one body but their soul determines what information is sent throughout the body. They can, however, feel a fraction of the others emotion and all of the other's pain.

Soriel will be involved. Don't make a big deal about it. It will most likely not play a large role in the story.