Tonkatsu is the healthy pig pet of the Cardboard Tube Samurai.
Originally found during the Cardboard and Steel saga, Tonkatsu later became the pet of the Cardboard Tube Samurai. He was told of the entire plan, so he would not be surprised when the villains attack.
Gabe also has a piggy bank named Tonkatsu; he was presumably cracked open for poker money at Tycho's insistence. The relationship between the two is unknown.
Tonkatsu is also the name of a Japanese pork dish.