[2] After spending 2009 with the Lions' farm team in the Eastern League, Asamura was a part of the first-team squad at the start of the 2010 season.

[8] He eventually succumbed to the injury and was removed from the Lions' roster on June 5;[8] he missed 6 weeks of play before returning just prior to the All-Star break as a pinch hitter on 15 July.

[12] Asamura had a limited pre-season but was at full health for the start of the 2015 season;[12] he maintained his fitness and missed only 2 of the Lions' 143 games.

[13] During the 2018 offseason, Asamura exercised his free-agent option and he agreed to a contract with Tohoku Rakuten Golden Eagles on November 21.

Asamura represented the Japan national baseball team in the 2013 exhibition games against Chinese Taipei and 2019 WBSC Premier12.