Prostitution thrives in the Hinodecho area of Yokohama, and I'm surprised no one else has posted information on it. The single floor establishments have the rooms in the back. The down side to this place is location.
Parking is scarce at times.
Also because of the windy streets and the sheer size of the place you may get lost, so use one of the tall hotel neon signs as a landmark. The women speak little or no english, but that doesn't appear to be an obstacle. You can find red-right zone in Yokohama. All of them are hookers. Girls are come from Thai, mainland China, Taiwan and HongKong.