Because of his elite contributions as a hitter and as a pitcher, a rarity as a two-way player, Ohtani's prime seasons have been considered among the greatest in baseball history, with some comparing them favorably to the early career of Babe Ruth.

The Fighters posted Ohtani to MLB after the 2017 season, and he signed with the Angels, soon winning the 2018 American League (AL) Rookie of the Year Award.

The 2023 final was one of the most-watched baseball games in history,[11] culminating with Ohtani striking out Angels teammate and USA captain Mike Trout on a full count, securing a 3–2 win and Japan's third title.

[15] He began playing baseball in his second year of elementary school, and as a seventh-grader, Ohtani recorded all but one of 18 outs in a six-inning regional championship game.

[20] Ohtani threw the pitch in the Japanese national high school baseball championship tournament, commonly called Summer Koshien.

[22] Ohtani expressed a desire to move directly to the major leagues after high school and received interest from numerous teams including the Texas Rangers, Boston Red Sox, New York Yankees and Los Angeles Dodgers.

[29] He was the second Nippon Pro Baseball rookie drafted out of high school the previous year to be used as both a pitcher and position player, following Kikuo Tokunaga in 1951; Ohtani was the first to start in both roles.

Ohtani received 4 of the 233 votes for the 2013 Nippon Professional Baseball Rookie of the Year Award (Pacific League), tying Tatsuya Sato for a distant second behind Takahiro Norimoto.

In a September 7 game against the Orix Buffaloes, he homered to straightaway center at Kyocera Dome to become the first Japanese player to reach double digits in both home runs and wins.

[36] During the postseason, Ohtani was chosen to become a member of the national team, dubbed Samurai Japan, and participated in the Suzuki All-Star Series,[37] a five-game friendly competition with a squad of major leaguers.

He started Game 5 at the Sapporo Dome and, although his team ultimately lost (3–1), he wasn't charged with an earned run (he gave up two unearned), and of the 12 outs he recorded in four innings, he got seven via strikeout.

[47] He led Nippon Ham to the 2016 Japan Series, but lost the opener to the Hiroshima Carp; he struck out 11 in 6 innings but allowed 3 runs, two on a homer by Brad Eldred and one on a steal of home by Seiya Suzuki.

In the bottom of the 10th, he singled off Daichi Osera score Nishikawa with the winner; Nippon Ham would take the next three games to win their second Japan Series title.

[57] Ohtani's debut MLB spring training in 2018 was disastrous and the majority of American news sources were extremely disappointed, concluding that he could not accomplish even one of his two-way abilities.

He became the second-fastest Angels rookie to reach 20 home runs, and he joined Babe Ruth as the only MLB players with 10 pitching appearances and 20 homers in a season.

[102] Additionally, in the same game, Ohtani became the first pitcher to throw a scoreless top half and record a hit, a RBI, a stolen base and a scored run while playing in an AL ballpark since Luis Tiant did so for the Minnesota Twins on April 26, 1970.

[105] On August 18, Ohtani hit his 40th of the year, becoming the first left-handed batter in Angels history to reach 40 home runs, surpassing lefty Reggie Jackson's 1982 record of 39.

[130] The Angels named him as the Opening Day starting pitcher[131] and he pitched 4+2⁄3 innings against the Houston Astros, allowing one earned run and one walk while striking out nine.

[133] Ohtani recorded two home runs, including a grand slam, on May 9, against the Tampa Bay Rays, marking the second time of the season and the eighth time in his career for Ohtani to record a multi-homer game, surpassing Ichiro Suzuki for the most by a Japanese-born player in MLB history,[134] The grand slam was the first of his professional career, including both NPB and MLB.

[140] On July 6, 2022, against the Miami Marlins, Ohtani made MLB history again by becoming the first player since RBI became an official statistic in 1920 to record 10 strikeouts as a pitcher, two RBIs as a batter, and a stolen base all in a single game.

[141] For a second straight year, Ohtani was voted into All-Star Game by fans as the starter at the designated hitter position[142] and he was selected as a starting pitcher again.

Ohtani joined Babe Ruth in an exclusive 10-homer, 10-win club; moved up on the all-time home run list for Japanese-born players; and set a single-season career high in strikeouts.

[150] Fresh off being named the Most Valuable Player of the 2023 World Baseball Classic, Ohtani made his second straight Opening Day start for the Angels' while batting third in the lineup against the Athletics on March 30.

[165] On August 23, he hit his 44th home run of the 2023 season but was removed from his start against the Cincinnati Reds after 1⅓ inning after experiencing what was initially reported as arm fatigue.

[188] On August 23, Ohtani stole second base in the fourth inning and hit his first career walk-off home run: a grand slam off Colin Poche of the Tampa Bay Rays.

[199] Ohtani made his postseason debut on October 5, in Game 1 of the National League Division Series, hitting a game-tying three-run home run in his second at-bat.

[205] In Game 2 of the World Series, Ohtani suffered what was initially described as a left shoulder subluxation when he slid into second base on an attempted steal in the seventh inning.

[217] He earned the save in the championship game after pitching the final inning of Japan's win over the US in the final, striking out his Los Angeles Angels teammate Mike Trout with a 3-2 slider to seal Japan's WBC championship, and won the tournament's MVP award after batting .435/.606/.739 as a hitter and posting a 1.86 ERA and 11 strikeouts in 9 2⁄3 innings as a pitcher.

[113] Ohtani also demonstrates elite baserunner skills, with a sprint speed and feet-first sliding technique allowing him to have been a league leader in stolen bases, bunt hits and infield-hit rate.

However, as ESPN prepared to air the interview on the morning of March 20, Ohtani's law firm issued a statement reading, "We discovered that Shohei has been the victim of a massive theft, and we are turning the matter over to the authorities."