Osaka Castle Hall previous concerts

Hi,
During a visit to Osaka 25th of May this year I passed the Osaka Castle Hall during afternoon. At the time there were a lot of people gathered for a kind of concert, unsure if it were in the Castle Hall stage but there were a lot of happenings going on outside.

I looked at the Osaka Castle Hall schedule through internet wayback machine but the only concert that day did not look like the name of the band or whátever it was going on outside. Is there any way to look at older schedules of things going on in Osaka?

probably, a concert of ketsumeishi
http://t2.pia.jp/feature/music/ketsume/index.html

Were you there on a weekend? Shiroten is the pathway/street leading up to Osaka-jo Hall and there are always street performers/indie bands/etc. along that path. It's a great place to hang out and listen to up and coming groups. Probably every band from Osaka has played there at some point.

Unsure if it was a weekend but it was a lot of people outside the hall and staff using megaphones directing people, and people wearing shirts and stuff with the group performers name. Might have been as ken suggests though.

Thanks for your replies :)