The Giants will likely carry two backup infielders behind starters Brandon Belt, Marco Scutaro, Brandon Crawford and Pablo Sandoval. Joaquin Arias should be a lock to fill one of those bench spots after hitting .270 as a fill-in for the injured Sandoval at third base and as a platoon mate with Crawford at shortstop last season.
The final infield reserve spot appears to be up for grabs between Tanaka, Brett Pill, Conor Gillaspie and minor league free agent Wilson Valdez.
Gillaspie is out of minor league options, but he's going to have a hard time making the team because he can't play the middle infield positions. Pill is similarly limited defensively to first base and left field, and the Giants are well-stocked at both positions between Belt and Buster Posey at first base and Gregor Blanco and Andres Torres in left field.
Valdez probably has the edge over Tanaka for the final spot heading into spring training because he has prior major league experience and the defensive versatility to handle shortstop. However, Valdez is a very limited offensive player who hit only .206 last year and just .236 for his career.
Tanaka, who will turn 32 next season, had two very good offensive seasons for the Nippon Ham Fighters. He hit .297/.379/.451 with 21 steals in 2008 and .335/.408/.417 with 34 steals in 2010.
He hit .300/.350/.363 last season, but missed time with a fractured elbow and ruptured UCL. He also missed most of 2011 with a fractured bone in his left foot that has since limited his ability to steal bases.
His contact ability, patience and defense should translate well to American professional baseball. He has won five Gold Glove awards and has been voted the best overall second baseman in the league via the Best Nine award four times during his career in Japan. His overall batting line since 2007 is .294/.366/.387.
His .387 slugging percentage and 26 home runs since 2007 suggest a lack of power, as does Tanaka's assessment of his own abilities. Tanaka said of his game, "I am not good at hitting home runs, and I have no power" (h/t Steve Sypa).
If nothing else, Tanaka is clearly a self-aware player who understands the limitations of his skill set. Listed at just 5'9", 170 pounds, Tanaka isn't likely to threaten Barry Bonds' single-season home run record if he does make the team out of spring training.
If Tanaka does claim a reserve job with the Giants, he would likely fill in for Scutaro when the 37-year-old veteran needs a breather. Given that Tanaka bats left-handed, the Giants could use him to spell Scutaro occasionally against right-handed pitching, and as a late-inning pinch-runner and pinch-hitter. Scutaro's advanced age could put him at risk for a trip to the disabled list next season, so depth at second base is a necessity.
The Giants have had success with these types of minor league deals in the recent past, with Blanco and Arias being the latest examples last year. All 25 roster spots are worthy of attention, and the Giants are busy creating spring competition for their remaining bench and bullpen spots.
These types of offseason moves aren't as exciting as signing a marquee free agent, but they could be the difference between winning the NL West and barely missing the postseason in the end.