Aoki was surrounded by a remarkable concentration of talent at Waseda: his year included shortstop Takashi Toritani (currently with the Chiba Lotte Marines), third baseman Toshimitsu Higa (Hiroshima Toyo Carp) and center fielder Shintaro Yoshida (Orix Buffaloes), all three of whom would later go on to the pros.

He hit .332 during his college career, albeit without a single home run, and was selected to the Tokyo Big6 Best Nine Award three times in his eight seasons (spring and fall) with Waseda as the starting right fielder.

However, he showed signs of promise in the minors, hitting .372 and leading the Eastern League in both batting average and on-base percentage (.436) and coming second in stolen bases (21).

2 hitter, striking out uncharacteristically often, he slowly began to collect hits at his usual pace and was promoted to the leadoff role by June 2005.

"[7] While major league teams expressed interest in Aoki (especially after seeing him in international play),[8] the Swallows offered no indication of their willingness to comply with the request.

[9] In 2007, Aoki and teammate and fellow outfielder Alex Ramírez competed for the batting title at a torrid pace throughout the 2007 season.

Meanwhile, his stolen base total dropped sharply from 41 to 17, a decline that could be attributed to then-player-manager Atsuya Furuta's placing Hiroyasu Tanaka (rather than Adam Riggs, as was the case in 2006), a second baseman with little power, behind Aoki in the 2-hole and instructing him to bunt often.

Aoki played in the Asian Baseball Championship as a member of the Japanese national team in December 2007, helping Japan clinch a berth in the upcoming Beijing Olympics.

However, he returned some three weeks later on May 29, 2008, engaging in another race for the batting title, this time with Yokohama BayStars left fielder Seiichi Uchikawa.

[12] In August 2008, Aoki was chosen to play in the 2008 Beijing Olympics along with teammate Shinya Miyamoto as a member of the Japanese national team.

[13] After he returned to the Swallows, manager Shigeru Takada opted to use him in the 3-hole permanently, slotting newly acquired left fielder Kazuki Fukuchi into the leadoff role instead.

He got hit in the head by a pitch thrown by Chunichi Dragons closer Hitoki Iwase on April 30, 2009, but was found to have no serious injuries upon diagnosis.

He made great defensive plays[20][21] and got big hits when they were needed, including a 2-out, 2-strike, 2-run home run on September 9, 2012, against St. Louis to tie the game and send it to extra innings.

[23] In 151 games in 2012, he hit .288 with 10 home runs, 50 RBI, 37 doubles, 30 stolen bases (9th in the NL), and 43 walks, giving him a .355 on-base percentage.

[26] On August 6, 2014, in a game against the Arizona Diamondbacks, Aoki hit a grand slam in the fifth inning off of relief pitcher Bo Schultz.

With a runner on third base and one out in the ninth after the Royals battled to trail 7–6, he hit a flyball deep enough in right field to score Jarrod Dyson to send the game into extras.

[31] On June 20, 2015, Aoki was hit by a pitch from Dodger Carlos Frias, breaking his right fibula and putting him on the disabled list, resulting in him missing 28 games.

Two weeks after his return on July 27, 2015, he was again hit by a pitch, this time in the batting helmet by Chicago Cubs pitcher Jake Arrieta.

[36] On July 31, 2017, the Astros traded Aoki and Teoscar Hernández to the Toronto Blue Jays in exchange for Francisco Liriano.

On January 30, 2018, Aoki signed a three-year deal to return to the Tokyo Yakult Swallows, where he spent the first eight years of his professional career.

After being relegated to the bench and seeing little playing time in the first two rounds, he was named the starting center fielder in the semi-finals against South Korea[44] and finals against Cuba,[45] but went 0-for-4 in those two games and finished with just one hit in five at-bats in the tournament.

3 hitter, he went 3-for-4 with a double and a walk in a 10–2 mercy rule win in the final game against Taiwan,[49] helping Japan clinch a berth in the upcoming Olympics.

Aoki played in all nine games in the 2008 Beijing Olympics as Japan's starting center fielder, batting in each of the first three spots in the order and hitting .294 (10-for-34) with seven RBI and scoring five runs.

He carried that same approach into the pros, going the opposite way for infield hits and singles to left field so often that teams began employing an "Aoki Shift", with the third baseman playing shallow and the shortstop shading the 5-6 hole, until 2006.

While most players shape their mechanics to perfection, Aoki does not hesitate to switch from one stance to another when he runs into hitless stretches (though he holds his bat much more upright than he did earlier in his career).

According to Statcast, Aoki's current batting stance positions his head closest to the assumed strikezone of any active player.

[citation needed] On the defensive end, Aoki has earned a reputation as a superb center fielder with excellent instincts and range, winning six consecutive Golden Glove awards from 2006 through 2011 and leading all outfielders in the Central League putouts in 2006 and 2007.