How the hell does one beat Takumi? He certainly seems OP as all hell, and 90% of the arena matches I have lost are because of him. I wish I had one of my own, but I have yet to get that lucky.
If you can bait him and finish with a unit that can ORKO, or have a Hector who can bait and watch Takumi suicide on enemy round. MRobin and Cecilia with default weapons and Triangle Advantage turn him into a joke. Some of the GHB horse units have weapons that grant ranged counter attack like Xander or Camus. Brave weapon units or Reinhardt/Olwen can also do the job in one round if he's in range.
Takumi was extremely popular at the start but I think it was the MRobin banner that pretty much made Takumi irrelevant. I still see him from time to time but he was nearly in every defence I faced when the game first came out.