The pairing of Dexter and Blossom and Buttercup's crush on Sensei Jack makes for a big in-joke once you find that Craig McCracken (The Powerpuff Girls creator) and Genndy Tartovosky (Samurai Jack) both worked together on Dexter's Laboratory!
Early in the comic, it's established that Jack came under the ownership of Courage after an elderly lady (Muriel) asked him to nurse the dog back to health...and never came back. For anyone who's familiar with the series, it's not hard to imagine what might have happened to Muriel...
