He made 26 appearances, including 14 starts, in Triple-A this year, going 5-3 with a 4.46 ERA.
The Bears said Flexen can dominate hitters with a fastball that touches 157 kilometers per hour, and he also throws a slider, a curve and a changeup.
KBO teams are each allowed to sign up to two foreign pitchers, and they had parted ways with both of their American hurlers from the 2019 season, Josh Lindblom and Seth Frankoff.
Lindblom, who was voted the regular season MVP after going 20-3 with a 2.50 ERA, is seeking a return to the majors. Frankoff was 9-8 and had a 3.61 ERA, and the Bears cut ties with him after the injury-plagued season.
To fill the one remaining foreign pitcher spot, the Bears are in talks with Raul Alcantara, who went 11-11 with a 4.01 ERA in 2019 with another KBO club, the KT Wiz.