This is a special stat for Super Sonico. She begins the training with 0. Unlike other stats, it is not listed on the stats page. You can only see it when it improves.
The guitar must be purchased in a random event while taking a walk to be able to improve this stat. It costs 300 Gold. When the stat reaches 10, there will be a scene the following morning which will activate the Perform Gig job.
1. ^ The text will show the the old value for the stat. The real value for the stat is the value shown + 2.