Soichiro-san is Kyoko's very old, fat, and dull-looking white dog. Kyoko adopted him to be her pet when he was found astrayed and followed his new owner to his new home by the smell of takiyaki. After living in his new surrounding for a few months, Kyoko brought Soichiro-san with her to Ikkoku-kan. At Ikkoku-kan, Soichiro-san dwells in a dog house outside by the front yard where he anxiously greets visitors to the apartment .

When Soichiro-san was first adopted, he was named Shiro, meaning white dog. Kyoko renamed her dog to Soichiro-san a few months later because she wanted the dog to act as a reminder to her life before Ikkoku-kan, something that she still can't let go. In fact, she felt so strongly about it that she nailed a sign with his name on top of the dog house so nobody would forget.