Looking to go into Kensai ASAP, looks like a Fighter could do it except for the skill requirements. Is there a way to get Concentration and Diplomacy as class skills for a Fighter? Regional feat maybe?

I could level dip into Paladin I suppose, but I'm trying to avoid being lawful good, lawful neutral seems more my style. There is a Paladin variant that allows lawful neutral but it also gives up Diplomacy and replaces it with Bluff.

Ranger could also be an option if I can just get Diplomacy as a class skill, but their combat style focus is ranged or TWF and Kensai only improves a single weapon so unless I'm using a double-weapon or bow, that is out. Is there a bow that can be used in melee in a pinch, maybe has a blade on one end? But I'm also intending to build a self-sufficient tank using the wrathful healing magic weapon ability so that limits me to melee only.

Looking to enter ASAP the prestige class kensai (Complete Warrior 49-52). It looks like a fighter could enter the class except for the required skill ranks. Is there a way—maybe by using regional feats—to get Concentration and Diplomacy as a class skills? Or are there other classes that more conveniently enter kensai quickly?