The Marlins were shopping Jacobs because he was due a big raise in arbitration, and have plenty of options at first base. In exchange, they got a right-hander who throws in the mid-90s.
"We are trading from an area of depth to an area we wanted to create more depth in," said Larry Beinfest, Marlins president of baseball operations.
Nunez, a native of the Dominican Republic, was 4-1 last year with a 2.98 ERA in 45 relief appearances. He has a 9-7 lifetime record in the majors.
This move was the first of several expected out of Florida, which has baseball's smallest payroll and 17 players eligible for arbitration this winter. The deal was actually completed much earlier, but the teams waited until the World Series concluded to announce it.
Jacobs is a career .262 hitter the Marlins acquired in the 2005 Carlos Delgado trade with the New York Mets. He had 32 home runs and 93 RBIs last season, both career bests, and helped the Marlins become the second team in MLB history with three infielders hitting 30 homers in a season.
"Obviously we like him a lot. He was among the top hitters in all of baseball last year, I think ranking 11th or 12th. And you know he plays in a really big ballpark," Royals general manager Dayton Moore said. "Has a lot of power to the middle of the field. Has a lot of energy, plays with enthusiasm, plays to win and he's a personality. He gives us a middle of the lineup presence."
Moore said Jacobs would probably bat somewhere in the No. 4 to No. 6 holes for Kansas City. Though the Royals have a crowd at first base, Moore said Jacobs would be in the lineup daily, either there or as the designated hitter.
The Marlins think they have cheaper options at first base in Gaby Sanchez, a 25-year-old who batted .314 with 17 home runs and 92 RBIs in Double-A last year. Also, they could play last season's third baseman Jorge Cantu at first and use Wes Helms or Dallas McPherson at third, Beinfest said.
Beinfest said the Marlins tried to get Nunez before. He said the 25-year-old pitcher, who also has a slider, could throw immediately out of the Marlins bullpen in late-inning setups.