Drafted into Pirates of Space (now MBCGame HERO) during the 2005 KeSPA rookie draft due to a lack of Protoss players on the team at the time, Bisu predominantly played in Proleague matches and Starleague qualifying matches during his first year and a half as a professional. Notably, he defeated Nal_rA, ChoJJa and Goodfriend during the early part of his career. By the end of 2006 he managed to obtain a career average of approximately 60% and was considered a solid player at the time.

Bisu burst into stardom after his stunning 3-0 defeat of sAviOr during the 2007 GOMTV MSL finals. During this time, he earned the nickname of "Revolutionist," forever changing the Protoss vs Zerg (PvZ) matchup. This was the most significant turning point of his career and the following months solidified his status as one of the greatest players of all time. During this period he managed to collect another MSL title by defeating Stork 3-2 in the finals, as well as a Starleague top 3 finish. His MSL streak was ended up a disappointing 3-1 loss to Mind in the Season 3 GOMTV MSL finals. Nonetheless, Bisu was also credited with reviving Protoss after years of Zerg and Terran dominance.

After leaving MBCGame HERO and signing with SK Telecom Team 1 in February 2008, Bisu entered into a slump; during this approximately half-year period, Bisu's win rate dropped to 50%. Bisu was knocked out of the individual leagues during their early stages and displayed disappointing Proleague results. In October 2008, Bisu broke out of this slump by going on a personal-best 12 game winstreak. As his performance continued to improve, he captured first place in the 2008 ClubDay MSL and first place for GOMTV Season 2 by defeating JangBi 3-1 in both finals.

After his two new titles, Bisu was disappointingly knocked out early from the following two MSLs (LostSaga and Avalon). His OSL "curse" culminated in the Batoo OSL, where his 11 game win streak was ended with a 3-0 upset loss to his teammate Fantasy. The overall strength of Bisu's play did not decline, however, and his win rate for the rest of the 2008-2009 Proleague season shot up to 80% (the best win/loss ratio of anyone), which contributed to SKT T1's first place finish for the regular season. SKT T1 would go on to win in the playoff finals against Hwaseung Oz, with Bisu winning his only game against Perfectman in day 1 of the finals. His achievements in the 08-09 Proleague regular season led him to win the title of MVP, sharing the award with Jaedong.

While Bisu was seeded into the 2009 Nate MSL and the 2009 EVER OSL, he was knocked out of the two leagues in the round of 32 and the round of 36, respectively. These results were seen as highly surprising due to his caliber of opponent. He was eliminated from his MSL group 1-2 with losses to Guemchi and Bogus and was knocked out of the OSL 1-2 by Shine. Bisu played up to his usual standard in the opening round of the 09-10 proleague, finishing with very strong stats of 7 wins and 2 losses. His two defeats came at the hands of Luxury and a relatively unknown Protoss, Haksoo. His sound play continued in round 2, finishing with an 8-3 record and ace stats of 1-1, the second best Protoss stats for the round alongside Jangbi. This leaves him at 15-5, some of the best stats going into Winner's league.