The Cosmic Papyrus

Papyrus grew up in a small town with his parents, hiding his skeleton features and extra arms from the universe. When strangers stumble into town they flip his world upside down and he runs for the nearest space shuttle, ready to leave it all behind and disappear. Years later he's rescued by another skeleton named Sans, and they travel the universe transporting shipments and other things. It's on one of these deliveries that they get pulled into an alternate universe, and they aren't the only ones either.