Well, I'm sure it's just purely by coincidence that she's using the sister's name as her streetwalking identity. Completely innocent. There have to be a million Rikos just within a few square blocks' radius of where they're standing.
Hold up... Are you saying that Riko was Aoi's first love? And Aoi began working as a prostitute under her first love's assumed name?
What kinda psycho does that?
@MrMcNasty It's called coping. I think she had a crush on Riko but Riko rejected her or she felt too insecure and disgusted with herself for falling in love with a woman (hence why she later ordered the prostitute). She chose Riko's name as a way to cope with her failure to soften the blow.