It seems Masahiro Yamamoto was ready to call it quits if he his start against the Hanshin Tigers on the 7th didn't go well.
In fact, based on what he told reporters it seems Yamamoto is ready to retire the minute he feels he isn't able to put up any results. He told reporters that he expected himself to win at least 3-5 games before the end of the current season (if not, it could mean retirement). Yamamoto also added that over the course of a full season, winning 10 games was important objective (if he returns next season and fails to win 10 games, it could mean retirement).
For the time being, it seems he's satisfied with the results, but the subject of retirement probably won't go away until he's completely satisfied that he's still capable of pitching.
Yamamoto's next start will likely be on the 14th against Hiroshima (just days after his 45th birthday on the 11th).