(Hemp Cloth #10)
This is a weird one.
The kanji can also be read as Mafu or Asanuno. The first kanji means “hemp, cannabis sativa.” One would guess the area was famous for hemp production, but to the best of my knowledge the area was famous for its horse market in the Edo Period. The area was home to the largest horse market in Japan. The Azabu area is divided into Moto-Azabu (Old Azabu), Nishi-Azabu (West Azabu), Higashi-Azabu (East) and Azabu Juban (Azabu #10), etc.
The legend goes that the 10th construction team of a number of teams working on bridges and sewage were stationed there. The name of their banner 十番 (#10) stuck.
Learn about Mita, which is right next to Azabu-Juban.