The Family Game Episode 10

Shinichi questions Sara why did Tago Yudai become Yoshimoto Koya. Yudai once told her that he does not want to repeat Souta's tragedy and wants help others like Souta to live strong. He learned that he can't stop all evil intentions in the world, but he can bring up people who can fight against evil intentions. That's why he became Yoshimoto. Not only that he prevented Shigeyuki from being the second Souta, but he also wanted to prevent Shinichi from turning into a monster like Yoshimoto. Sara gave him Yudai's notebook which has written notes about the Numata family.