As far as I know, Yokosuka City in Kanagawa Prefecture is the only city in Japan that has a manhole design featuring a gaijin. The foreigner in this case is Commodore Matthew Perry, an American naval commander who played a leading role in the opening Japan in the 1850s. The ship depicted in the background is one of the "black ships", or kurobune. These were ships of western origin that started appearing menacingly in Japanese waters in the 19th century. Perry's ships first arrived off the coast of Uraga which is to the south of Yokosuka.
This is another more common design for Yokosuka's manholes. The star in the center is the city's seal and the flower is the city's official flower, the hamayū (ハマユウ) or Crinum asiaticum (also called Poison Bulb, Grand Crinium Lilium).
An underground fire hydrant.
Another fire hydrant. Fairly standard design, this one.
An air valve, whatever that is.
Commodore Perry, himself.
The Japanese Battleship Mikasa.