Once you are down the stairs, everything is in the same room. There is an elevator that is occasionally used for loading in so I suppose if you ask the venue, the will let you use it if you have a wheelchair. Sometimes they also have benches to sit on and a few rickety stools.
One moderately long set of stairs (20-25 stairs) to get the venue as it is in the basement of a building.
The bathroom is attached to the room where the bands play so it is easily accessible. However, it is a Japanese style toilet, so you cannot sit down.
3-14-5 Nanbanaka, Naniwa Ward, Osaka, Osaka Prefecture 556-0011 Japan