Who is Kikuhiko (the man) from A Personal Matter and what is their importance?

Kikuhiko was abandoned by the selfish, irresponsible Bird as a youth. He later encounters Bird, and their conversation plays an important role in defining and/or triggering the final stages of Bird's journey of transformation. Through their conversation, Bird realizes he has been acting out of fear for much of his adult life, and that it's time to move past that fear (particularly the fear that his life is about to be completely absorbed by his child) and accept responsibility that he didn't necessarily seek, but ultimately has no choice but to accept.