The Nippon Professional Baseball (NPB) playoffs have taken several different forms throughout the organization's history. Japanese baseball is divided into two leagues; the Pacific League (PL) is less popular and less profitable than the Central League (CL). As a result, the PL has employed various playoff formats throughout its history in an effort to increase fan interest. The PL's first true playoff system was introduced in the 1973 season. It involved a split season plan that divided the season into two halves and the two teams that won each half went on to play each other in a five-game playoff series, with the winner advancing to the Japan Series. While popular with fans, the format was scrapped after ten seasons because of major issues and criticisms. In the year following their last split season, the PL returned to a single season, however if five or fewer games separated the first- and second-place teams at the end of the season, the two teams would play each other in a five-game playoff series. This playoff system was unpopular and ridiculed by media and fans. It only lasted three seasons with a playoff series never needing to be played.

With their first two playoff systems abolished, the Pacific League returned to simply advancing their regular-season champion directly to the Japan Series. During this time, the PL's Seibu Lions won six Japan Series championship titles in seven seasons from the mid-1980s to the early-1990s. After the fall of the Lions in the mid-1990s, the league struggled to win championships against the Central League and lost three consecutive Japan Series to start the 2000s. Again fighting for its survival as its popularity faded, the PL board of directors agreed to reintroduce a playoff system to be used in the 2004 season to potentially create more regular-season excitement. The new postseason plan initiated a two-stage playoff in which the top three PL teams competed. In the First Stage, the teams that finished the season with the second- and third-best records played each other in a best-of-three series. The winner of this series faced the league's top finisher in the second, best-of-five stage. The winner of the Second Stage advanced to the Japan Series, where they competed against the CL's regular-season champion. After two years, the rules were changed to award the first-place team an automatic one-win advantage in the Second Stage. Though Central League officials initially criticized the plan, the PL's playoffs were a success and soon after the CL was criticized for not implementing a playoff system of their own.

Unlike the Pacific League, the Central League had never experimented with any type of postseason system prior to 2006. They had situational playoff scenarios written into its bylaws in the event of an end-of-season tie, however, it never occurred and a permanent playoff plan had never been created. In 2006, encouraged by the success of the PL's postseason system, CL officials announced their intention to introduce playoffs for the 2007 season to help boost declining attendance. Later that year, PL and CL officials agreed on a unified postseason system. The CL implemented a playoff system identical to the PL's, and the entire playoff series was dubbed the Climax Series, NPB's current playoff format. The PL agreed to name the regular-season first-place finishers league champions rather than the team that won the leagues' respective playoffs—a reversal from the previous three seasons. The two leagues also agreed that neither regular-season champion should receive a one-game advantage in the Final Stage of the Climax Series. However, after one season, the leagues overturned their decision on the Final Stage advantage and agreed to award their champions a one-win advantage in the Final Stage starting with the 2008 Climax Series. At the same time, the Final Stage changed from a best-of-five series and became a best-of-seven series, where the first team to accumulate four wins advances to the Japan Series.

Pacific League playoffs The Pacific League (PL) first experimented with a type of end-of-season playoff system during the 1952 season. After the 108-game season had concluded, the teams with the four best winning percentages qualified to play in a twelve-game round robin stage in which each team would play three games against the other three qualifying teams. The results of these games were then added to the teams' regular-season results to determine the league's champion. After all 120 games had concluded, the Mainichi Orions and the Nankai Hawks both had 75 wins, however the Hawks had one less loss than the Orions because of a game against the Daiei Stars that ended in a tie earlier in the season. Because of the impact the tie had on the pennant race, the Hawks and the Stars played an extra 121st game. The Hawks won the game, giving them sole claim to Pacific League title and the right to represent the PL in the Japan Series. After the season, this faux playoff system was abandoned because of criticism that it was unfair to the three non-qualifying teams that had their seasons truncated.

Split season (1973–1982)

During the Pacific League owners' meeting on November 20, 1972, a split season plan that included a potential genuine playoff series was approved for the 1973 season. Less popular and less profitable than Nippon Professional Baseball's (NPB) other league, the Central League (CL), the PL hoped that the new format would significantly increase fan interest. The season was divided into two, 65-game halves. The two teams that won each half went on to play each other in a five-game playoff series. The winner of the series was named the PL champion and went on to play the Central League (CL) champion in the Japan Series.

Playoff games under the split-season format were commercially successful and often played to sold-out crowds, a rare occurrence during the Pacific League's regular season. The format, however, had several problems and criticisms. While it did create two potential playoff races in one season, dead rubber games that had no playoff implications still resulted once a team clinched each half-season title. Furthermore, it allowed a team with only the third-best winning percentage for the full season to reach the playoffs and the Japan Series. The Seibu Lions' manager during the split-season format's final season, Tatsuro Hirooka, heavily criticized the playoff system for this reason. He believed teams could potentially abuse the format by focusing on the first half alone instead of the full season. Then, once a team became the first-half champion, it could rest players during the second half as their playoff berth had already been guaranteed. Another problem specific to the split-season format is that the playoff series was cancelled if one team won both half seasons. This occurred twice in the 1976 and 1978 seasons. These issues led to the format being scrapped after ten years and replaced for the 1983 season.

Results In the 1973 season, the first year the system was implemented, the Nankai Hawks clinched a playoff berth by winning the first half of the season, however they finished the full season with only the third-best winning percentage in the league. It was the only example during the split-season era in which a team without the top-two highest winning percentages won the playoff series and advanced to the Japan Series. In the 1976 and 1978 seasons, the Hankyu Braves won both half-seasons nullifying the need for playoff series. Of the eight playoff series that were played, the first-half champion won five of them.Bjarkman 2005, p. 143

+ Pacific League Playoff results (1973–1982)YearFirst-half championRecordSecond-half championMost Valuable PlayerFighting Spirit Award1973Nankai Hawks*2–1Hankyu BravesMichio SatoTaira Sumitomo1974Hankyu Braves0–3Lotte Orions*Choji MurataTokuji Nagaike1975Hankyu Braves*3–1Kintetsu BuffaloesTokuji NagaikeArita Shuzo 1976 ZPlayoff series was not needed because the Hankyu Braves won both half-seasons1977Hankyu Braves*3–2Lotte OrionsHisashi YamadaMasaharu Mitsui 1978 ZPlayoff series was not needed because the Hankyu Braves won both half-seasons1979Kintetsu Buffaloes*3–0Hankyu BravesTetsuji YamaguchiMitsuo Inaba1980Lotte Orions0–3Kintetsu Buffaloes*Mitsuyasu HiranoMichiyo Arito1981Lotte Orions1–1–3Nippon-Ham Fighters*Junichi KashiwabaraChoji Murata1982Seibu Lions*3–1Nippon-Ham FightersTakuji OtaMikio Kudo The team won the series to become the Pacific League champion and advanced to the Japan Series. BOLD: The team went on to win the Japan Series.

Five-or-fewer games separation (1983–1985) In 1983, the PL returned to a single, 130-game season, however if five or fewer games separated the first- and second-place teams at the end of the season, the two teams would play each other in a playoff series. The winner of the five-game series would be named the League champion and represent the PL in the Japan Series. This implemented a playoff system that was unpopular and uniformly ridiculed by most baseball media and fans. While the system removed the possibility of a team with a low regular-season winning percentage advancing to the Japan Series, it also removed the excitement of a close pennant race near the end of the season. It forced a winning team that narrowly beat its second-place competitor to try and defeat them again in a playoff series. The system only lasted for three seasons with a playoff series never needing to be played.

Playoffs (2004–2006) After the Pacific League abolished their first two playoff systems, the league returned to simply advancing their regular-season champion directly to the Japan Series. In this era before interleague play, the Pacific and Central Leagues vied for supremacy via the Japan Series. From the mid-1980s to the early-1990s, the PL's Seibu Lions entered their "Golden Age", winning six Japan Series titles in seven seasons. After the fall of the Lions in the mid-1990s, the Pacific League struggled to win championships against the Central League. To start the 2000s, the PL lost three consecutive Japan Series and was fighting for its survival as its popularity faded. When a first-place team had a substantial lead in the standings near the end of a regular season, there was no pennant race leading up to the Japan Series and fan interest and excitement waned. In an attempt to rectify this problem and increase the league's overall popularity, the PL board of directors agreed to reintroduce a playoff system to be used in the 2004 season to potentially create more regular-season excitement. The new postseason plan initiated a two-stage playoff in which the top three PL teams competed. In the First Stage, the teams that finished the newly shortened, 135-game regular season with the second- and third-best records played each other in a best-of-three series. The winner of this series faced the league's top finisher in the second, final stage. The Second Stage winner advanced to the Japan Series, where they competed against the CL's regular-season champion. Games could end in a tie if there was no winner after twelve innings. In a case that resulted in a series tie, the team that had the better head-to-head regular-season record advanced. The winner of the playoff series was named the Pacific League champion instead of the team that finished the regular season in first place. After the announcement, CL officials criticized the plan, with Giants' owner Tsuneo Watanabe going as far as to proclaim that if the PL team that placed third during the regular season advanced to the Japan Series, his team would refuse to play in the Series.