He was drafted by the Royals in the 15th round of the 2002 Major League Baseball Draft. He played for the Gulf Coast Royals in, Single-A Burlington Bees in and, and the Single-A Advanced High Desert Mavericks in. In, he played for the Double-A Wichita Wranglers. Kaaihue split between the Single-A Advanced Wilmington Blue Rocks and Wichita. In, Kaaihue played for Kansas City's new Double-A affiliate, the Northwest Arkansas Naturals. There, he led the minor leagues in walks, with 104. He also played for the Triple-AOmaha Royals. When rosters expanded on September 1, 2008, Kaaihue was called up to the major leagues. He made his major league debut on September 4,. He hit his first major league home run on September 20, 2008. , triple-A affiliates of the Kansas City Royals, in Kaaihue spent the entire 2009 season in Omaha. He began the 2010 season in Omaha, and was called up to Kansas City in May. In his first Major Leagueat bat that season, he pinch hit for Willie Bloomquist in the 8th inning of a May 6 game against the Texas Rangers, and hit an RBI single that broke an 11-11 tie. After having a disappointing start of the season Kila started getting hot finishing the 2010 Royals season with 8 home runs and 25 runs batted in. Kaaihue started the 2011 season as the regular first baseman for the Kansas City Royals. He hit a walk-off home run on April 1 as the Royals beat the Angels 2-1. Mired in a hitting slump from the start of the season, averaging just.195 in 23 games, with only six RBIs and two homers, Kaaihue was optioned to Triple-A Omaha on May 5. Eric Hosmer was called up to replace him. He was designated for assignment on September 21, 2011.
Oakland Athletics
On September 27, 2011, he was traded to the Oakland Athletics for minor league pitcher Ethan Hollingsworth. On June 6, 2012, he was designated for assignment. In 39 games for the Athletics, he hit.234/.295/.398 with 4 HR and 14 RBI.
On November 21, 2012, Kaaihue signed a minor league contract with the Arizona Diamondbacks, but was released from the Reno Aces, Arizona's Triple-A affiliate, on June 1, 2013. He led the Triple-A Pacific Coast League in home runs.
Hiroshima Toyo Carp
On June 15, 2013, Kaaihue signed with the Hiroshima Toyo Carp in Japan.