In the middle and late stage of the game, after the protagonist of Qionghua School changed back to his original costume (the reason is not explained, so as not to cause spoilers), the shadowless sword tactic can play a normal role in the battle.
In fact, at the usual training speed, you can't learn the shadowless sword tactic in the stage before changing back to clothes, because the training is too hard and you practice it in advance, but it can't be used because of bugs. ...