Koyo Aoyagi grew up drinking Yakult products. His mother and brother work at Yakult and he spent time in the company nursery until he was about three.
Aoyagi threw from about three-quarters the first time he played catch for the Terao Dolphins when he was fifth year elementary school student. The manager of the team tried to fix his mechanics, but eventually decided to encourage him to keep throwing from the side.
Source: Sponichi 12/13/2016
Aoyagi is an avid manga fan. When he first joined the Tigers, he moved into their dormitory with about 300 mangas. Publisher Kodansha is thinking about naming him their managa publicity ambassador.
Source: Nikkan Sports 12/18/2016