Do you know why he keeps the dog? Because deep inside, Batou is ronery. Sure, he works with Makoto and Togusa, but it is just that, work. He knows that even though Major constantly flaunts her sexy hips in front of him she is still more intrested in Net than anything else and Togusa is techonphobe. So every night after holding up his facade at work he goes into his home where he would weep himself into sleep if it wasn't for the loyal dog.