Happy Birthday Part 1

It starts with man who looks like Bossun, yet viewers find out that he is Ryōsuke, Bossun's father. In the present, Bossun recalls finding old tapes and learns about his father. When Akane comes home, she finds Bossun watching the tapes, so she quickly locks them up. Desperate to know the truth, Bossun goes through the photo albums. What did Bossun uncover about his father and Akane's secret?