Akira kept his stubborn attitude, but he had nothing to say back. Mainly because Roku was right. And a little because he really didn't know how to use the microwave. He was just annoyed because Roku was acting so high and mighty about knowing stuff that was normal for him but new to Akira. Actually Akira wouldn't know whether or not Roku was really acting like that, he doesn't know enough about other people to be able to judge that.