He is the only one that learned from his mistake of misleading the MC. I really respect the friend here, took his L learned WHY MC is the way he is and wants to do better by him.
Ainosuke is Tsuyoshi's final lifeline, the last thing preventing his heart from breaking. I feel if things go wrong here then Tsuyoshi will get seriously fed up will all 3 countries and snap for real. He had an emotional outburst already but if he decides that these people only listen to violence then he probably will feel forced to speak with violence.
After all that shit talking, the old man actually decides to dodge the first punch. I guess there has to be some sort of limit on how much damage the weirdo could take and when it comes to Damage output our Karate Bro is MORE than ready