Disclaimer: This is an expansion on a point I made in my first blog post. It is copied from two comments I made on Book 12's page. This is purely my opinion and it is not to be taken too seriously.
Rant[]
Even to this day I’m still bitter about what happened to Captain Underpants in this book. He got erased from Mr. Krupp's brain, essentially KILLING him. And to make it worse, George and Harold don't care that he is gone forever and forget about him by the next page. This implies the readers weren’t supposed to see Cap's death as a big deal, or maybe Dav intended it to be a GOOD thing.
Oh, and Yesterday George and Yesterday Harold never find out about Captain Underpants' fate until adulthood, and even then they don’t care. When they go to the treehouse, they decide to stop making Captain Underpants comics in favor of Dog Man ones. So this means Captain Underpants is completely dead and forgotten, even in comic form!
Captain Underpants helped save countless lives and protected George and Harold from danger numerous times, and THIS is what he gets for all he has done?