Players may have noticed that Ringo was no longer the same person when the main game started after the prehistory. But what happened in this "missing" year? When you recall your memories, it's usually not so easy to pinpoint the exact day when something went differently. Although Ringo had "that day" later, there were a lot of little things about this missing year that gradually changed him.
And to give you an example, I want to share with you the day Ringo quit karate in this manga. Maybe this will clarify something about Ringo for you, or at least give you some hints.
Location: \steamapps\common\The friends of Ringo Ishikawa