Jankara ( ジャンカラ) is a chain of Karaoke all over Japan. In Umeda/Osaka alone you can almost find them in every corner BUT did you know that you can also wear cosplay costumes while singing your heart out ?
Ohatsu Tenjin Branch ( お初天神店 ) in Osaka have this option. Cosplay costumes are free though they are not exactly clean, there are also some wigs available.
Oh and sizes are a bit small too ..