The 21st Competition, official name: SASUKE2008秋 (literally Sasuke 2008 fall), is the fourth tournament since Nagano Makoto's kanzenseiha in SASUKE 17, and the tournament in which Urushihara Yuuji made his debut. Prior to this tournament, preliminary trials were held in both Japan and the United States. The SASUKE 21 Trials had eight representatives and the United States had six (although only three actually qualified). Due to the poor results of the last two tournaments, the course was kept virtually the same. In fact, only one new obstacle, the Hang Climbing, was introduced. The results in this tournament were vastly better than SASUKE 19 or SASUKE 20 as 9 people cleared the First Stage, including the last four consecutive competitors (a Shin-Sasuke record). In the Second Stage, the Salmon Ladder eliminated four of the nine, and only three were able to clear. Two-time Pro Sportsman #1 champion Miyazaki Daisuke cleared the First and Second Stages for the first time but failed the Devil Steps in the Third Stage, the earliest third stage failure in Shin-Sasuke. In his record-breaking 11th appearance in the Third Stage, Takeda became the first person to clear the Shin-Cliffhanger. Nagano made it to the final obstacle in the Third Stage, the Gliding Ring, where a flaw in design made the obstacle much more difficult than imagined. As a result, Nagano failed there, ending the tournament. For an unprecedented fourth straight tournament, no one made it to the Final Stage.
This tournament marked a return to dominance for the SASUKE All-Stars as all five who competed made it to the Soritatsu Kabe, three of them cleared the First Stage (the most since SASUKE 17), and Nagano and Takeda cleared the Second Stage.