I got inspired for this yesterday.
An explanation is order. I know almost nothing about Viper's AU, including the name. All I've seen are Sans Comic TV's "Try not to laugh" and "Try not to cry" challenges featuring these characters. Which is a shame, because I love these guys! I became further confused when Viper was sometimes depicted with Rex as his brother and other times with Pup. (Cutest little guy...!) After seeing a video where Rex lost his temper with Viper and hit him, and then fussing over him looking a lot like Pup, I developed this headcanon.
Rex and Pup are the same person and have Split Personality Disorder. Most of the time he's Rex, but sometimes Pup just wants to be the young kid he really is... like right now, when he just wants to watch a little kid's show. This puts Viper in a strange situation where he takes the role of Rex's younger brother but also Pup's guardian who keeps him out of trouble! Oh, my gosh, I love Pup so much! EE!
This is going to be a micro-series by the way. This illustration I did of Red and Blue together is actually the first strip.