Kojima lived near the sea in Tsujido until he was three, and after…

Kojima regarded the primary family form as a unit of four: his parents, his brother two years older, and himself. After moving from Tokyo toward Kansai, his parents built a house in 1970 in a new development in Hyogo, distant from grandparents and other relatives; Kojima’s father presented that house as where they were starting and from which their children could also begin. They did not have the typical suburban dog because Kojima’s mother had asthma.

As his eldest son grew, Kojima stopped visiting Kamakura and likewise became too lazy to go back to Kobe; Umimachi Diary reminded him of what he had lost and what he must not forget. At the end of that summer he went to Hayama with his younger son, and from the train saw the sea where he had played with his father and where he had gone with his first son, and he decided to resume that diary of outings when the younger son is old enough.

Kojima recalled that when his son was small they did all kinds of activities and trips together, but that abruptly ended when his son started junior high and preferred to be with his friends. Since Kojima's own father died when he was thirteen and he had no experience of going through adolescence with a father, he said he did not know what closeness or distance to adopt with his son; he sought guidance by rereading Early Autumn.

“My home was close to the sea, and it left a very strong impression on me.”

Kojima went with his teenage son, a Hanshin Tigers fan, to a Giants–Tigers game; Kojima drank beer and his son drank orange juice, and although Kojima was not interested in baseball he used the pauses in the game to ask about and listen to his son’s life, considering those conversations their version of a father–son game of catch.