This week’s slate of NPB games marks the start of the 20th edition of interleague play in Japan.

Japanese baseball introduced interleague competition in 2005, giving fans a chance to see Central and Pacific League teams compete outside of the annual Japan Series matchup. It happens during a set period each year — June 3 to 22 this season — and the team with the best record is crowned champion at the end.

While the format has gone through a few iterations since 2005 (and was canceled in 2020 due to the COVID-19 pandemic) the one constant has been Pa League dominance.