Koji's groove charges much too slow for how weak his groove is. In however many games I've chosen him I've rarely, if ever, achieved groove before the game ends. If Koji attacks a village for groove charge, over the two turns it takes to turn the village to neutral he still only has 45% charge by that point. In comparison, Emeric can already have his groove ready by that same turn following the same village attacking strategy. Koji's strategy is very long term, but the thing is, games often never go that long anyway. There's often very little incentive to be that aggressive with your commander to achieve groove. Koji can only be good on maps where he can attack gates and enemy villages for groove. Either his groove should be more powerful, or it should charge more quickly.