"seme whose attachment to the uke is so much like that of a puppy or a dog, so full of
devoted love, that he is partly drawn with a wagging tail and doggy ears as a visual pun..."
(the term "hachi-tachi" is a new word creation of Slykitty)
http://www.mangago.me/home/mangatopic/710037/ at the end of the list are dog-like ukes too...
