Now THIS is a good material for a final boss. Not only was he obviously evil or at least suspected to be the true villain very early on, but when it is time for the reveal, he exceeds expectations in a different way, and no, it is not by showing the opposite, which is revealing that he is not evil all along. But by showing his reasons for doing the things he did, how he did it, and his determination on going down that path. While Tsurugi did defeat him in this episode, you can already guess that we haven't seen what he is truly capable of. See, sometimes it is best to show the villain very early on, including the final boss.