Before the Brewers
For eight years Nori Aoki was something of a superstar in Japan with the Yakult Swallows. In his first full season--2005--he won the NPB Rookie of the Year award. Then he went on to win 3 batting titles and 6 golden gloves. He was a 7 time NPB All-Star. He also won something called the "Best Nine Award" a stunning 9 times. It's essentially an award given to the best player at a position--one for all three OF spots--as voted on by sports writers.
It's nothing short of a stellar career and one that doesn't really seem to line-up with the paltry sum the Brewers posted to get exclusive negotiating rights. They won with a posting bid of just $2.5 million. As a result the Brewers were able to sign Aoki to a 2 year deal worth just $2.5 million with an option year at $1.5 million.
With the Brewers
The Brewers entered the 2012 season expecting Nori Aoki to serve as their back-up outfielder. However an injury to first baseman Mat Gamel forced the Brewers to get creative. They transitioned right-fielder Corey Hart to first and gave Aoki more playing time. It proved to be a great move for the Japanese outfielder.
In very little time Aoki proved that his skill set worked in MLB. That year he hit 288/355/433 with 10 home runs and 30 stolen bases. His production was worth a 113 wRC+ and in total he earned 2.3 fWAR. That pretty solid for a player making just twice the league minimum who was expected to be the 4th or 5th best outfielder on the team.
His second season with the Brewers was still decent but it was a step down. He hit 286/356/370 with 8 home runs and 20 stolen bases. He also hit 17 less doubles. Both his power and speed took a step back. He went from a 113 wRC+ to a 102. He also accrued just a 1.5 fWAR.
Personally I think he was still worth starting that year because his OBP was still strong. But with the emergence of Khris Davis the Brewers felt Nori Aoki was expendable with just one year left on his contract. During the offseason they traded him to the Kansas City Royals for left-handed pitcher Will Smith thus ending Aoki's time in Milwaukee.
After the Brewers
Nori Aoki played one season with the Kansas City Royals. Lucky for him it was the season they went to the World Series. He was much the same player he was in his second season with the Brewers. He hit 285/349/360, 102 wRC+, and 2.3 fWAR. He only hit 1 home run and stole 17 bases. Again, it was a decent season but not quite as good as that first year.
After his season with the Royals the Giants signed him to a one year deal worth $4 million with an option year. Nori Aoki is nothing if he's not remarkably consistent. With San Francisco he hit 287/353/380, 112 wRC+, and was worth 1.5 fWAR. He hit 5 home runs and stole 14 bases.
Free Agency Outlook
At the end of this season the Giants decided to decline Aoki's very cheap team option--$5.5 M with a $0.7M buyout--allowing Aoki to enter free agency for the second time of his MLB career. Unfortunately for Aoki he enters free agency in a year where there are just a ton of solid outfield options. He has four years of MLB service time now but none of his seasons have been excellent. On top of that he's a no-power corner OF with decreasing speed and just okay defense. He may have to settle for just a one year deal and it might be as a team's 4th outfielder.
However if a team needs OBP they could view him as a super cheap option and give him a 2 year deal. He's unique in that I doubt he beats that deal San Francisco game him. Which means he's going to be really cheap. So a team could sign him as a stop gap--if they have a prospect year or less away--and then transition him to a back-up role when that prospect is ready.
Statistics and contract information courtesy of FanGraphs