Soichiro is Kyoko Otonashi's pet dog. He serves as the perfect hindrance to Shun Mitaka's pursuit of Kyoko.

Spoiler

He was first found as a stray by Soichiro Otonashi. His original name is "Shiro" ("Whitey"), but he only responds to the name "Soichiro" and so Kyoko insists on calling him "Soichiro" in memory of her husband. He is always in danger of being lost because of following food carried by strangers.