Wanpo is a rather large and lazy dog, possibly a mix between an Akita and an Alaskan Malamute (according to Morikawa himself). He was given to Ippo as a puppy by Nekota as a simultaneous commemoration of both his 20th birthday and his acquisation of the JBC Featherweight Championship. He is Hachi's son and plays with his father when he appears. He makes an oddly serious looking face when defecating, first shown when he is given to Ippo. At that time he ended up defecating on Ippo's then-brand new belt, earning the nickname Pooping Champion (ウンコチャンピオン, Unko Chanpion).
After growing into adulthood, he has come to greatly resemble Hachi. He also got fatter, and as a result no longer joins Ippo during his road work. He has taken a great liking to Kumi and often humps her whenever she appears.
Named by Ippo's mother, his name is a pun on Ippo's own name. Ippo (一歩) means One Step in Japanese, while Wanpo is merely replacing the character for One (一) with the English word One (ワン, Wan).