Train with Yoru (Only during Weekends I think) a few times and you get an OP skill called Blade sweep, to train just go to the forest and train, the first 3 times you will lose ( don't worry it's scripted)and You'll get a new supporter in your team, I think Ami is the name, after the 3 times you can train your skills like that. I strongly suggest you finish both the forest Explorations as in the end Ami unlocks a very powerful insta heal but requires 5BARS