Apropos of nothing, I wonder of the Koji signing might in a small way be related to courting Otani. There's not a lot of japanesse players in the majors/minors right now. Using out of the park 17 to quickly judge we're talking about Junichi Tazawa with the red sox, Koji obviously, Tanaka with the Yankees, Ichiro, Yuhei Nakaushiro with Arizona, Toru Murata with Cleveland, Kenta Maeda with the dodgers, Kawasaki who was last with the cubs, Hisashi Iwakuma with the M's, Nori Aoki also last with the M's, and Darvish with the Rangers. If I'm not mistaken that's the entire list.
I have to believe that those guys would largely be pretty close nit given they are a some what small group and they all share a common culture. Assuming Koji and Kawasaki have enjoyed their time on the cubs that really couldn't hurt and assuming the monetary situation all being equal it's reasonable to expect Otani to consult that group of guys about their experiences thus far.
That's not to say I think that was the primary motivation behind signing Koji. I think he's likely to be an effective guy and possibly really good out of the bullpen. But as an added side benefit, it probably doesn't hurt having some name recognizable japanesse players playing for you before courting one of the biggest to come over in some time.