This novel is about a man who confronts or actually tries to run away from every step towards adulthood. As his wife is about to give birth to their first child, Bird is confronted with responsibility that he starts to actively run away from. Bird, a nickname to indicate his immaturity, is at a crossroad of either choosing to continue running away from adulthood responsibilities or to grow up and become a responsible grown up.
In fact, the story is primarily spent dealing with Bird preparing to run away. It was interesting. I find that this appears to be a common trope in Japanese Literature whether it be male or female. They are rebelling against the expectations of adulthood and are lost.
This story is full of angst and the struggle of coming to terms with adulthood and being an active participant in life rather than coasting through it.