As per usual, the top-flight side, in this instance Köln, will go into the matchup as significant favourites. Since the 2010-11 season, only two 2. Bundesliga teams have won promotion, with them being Fortuna Düsseldorf in 2012 and Union Berlin in 2019.
Die Geißböcke also have momentum on their side. They've been quality since Friedhelm Funkel's appointment at the start of April, winning three big matches, including a 2-1 victory against RB Leipzig. Not only has Funkel provided an improvement in results, the performances have seen a significant upturn as well. The football has been much more free-flowing than it was under previous manager Markus Gisdol, who opted for a more pragmatic, counter-attacking playstyle.
For a while it looked like Köln would be heading for direct relegation to the 2. Bundesliga, but a last day win against already-relegated Schalke meant that Werder Bremen dropped down to the second tier instead.
Kiel, meanwhile, enter the play-off after a late-season collapse. Going into their final two games of the 2. Bundesliga campaign, Ole Werner's side were sat in 2nd place, and they only needed one win to go straight up. However, defeats against Karlsruher and Darmstadt opened the door for Greuther Fürth, who took Kiel's place on the final day, sending Die Störche into this matchup as a result.
For Köln, the only absentee is Sebastian Andersson, who is dealing with a knee injury that has hampered him for most of the Rückrunde.
As for Kiel, Mikkel Kikeskov has a broken hand and Ahmet Arslan is out with an ACL injury, so neither will feature.
Köln - Timo Horn; Benno Schmitz, Rafael Czichos, Sebastiaan Bornauw, Noah Katterbach; Ondrej Duda, Salih Özcan, Jonas Hector, Ellyes Skhiri, Ismail Jakobs; Jan Thielmann
Holstein Kiel - Thomas Dähne; Jannik Dehm, Simon Lorenz, Hauke Wahl, Johannes van den Bergh; Fin Bartels, Benjamin Girth, Niklas Hauptmann, Lee Jae-sung; Janni-Luca Serra, Fabian Reese
Köln - WWLDW - last game - 1-0 (W) vs Schalke
Holstein Kiel - WWWLL - last game - 2-3 (L) vs Darmstadt
Ones to watch
Köln - Left-back turned centre-mid Jonas Hector has been with the club since 2010 and has spent the entirety of his professional career at the RheinEnergieStadion. Suffering relegation in 2018, the then-Germany international stayed with Die Geißböcke and helped them make an immediate return to the Bundesliga. Would he do the same this time around if Köln are ultimately beaten by Kiel? Only time will tell.
Holstein Kiel - Fin Bartels is a familiar name to some Bundesliga fans, mainly those of Werder Bremen, his former club. As they head down to the second division, Bartels could take the team he joined last year from Die Grün-Weißen to the top-flight. The 34-year-old, who is a Kiel native, has been in scintillating form this season, with his 17 goal contributions in the league playing a key part in his team's promotion push. Bartels was huge in Die Störche's famous DFB-Pokal win over Bayern Munich earlier in the campaign, and there's a chance that he could be just as big on this occasion as well.
These two sides have only met twice, and those games came during the 2018/19 campaign, Köln's last in the 2. Bundesliga.
They drew 1-1 in Kiel before Die Geißböcke ran out comfortable 4-0 winners at the RheinEnergieStadion in the reverse fixture, with the aforementioned Jonas Hector scoring and providing an assist in that encounter.
How to watch
This contest will air on BT Sport 2 at 17:30 BST in the UK, while those in the United States will be able to watch the game on ESPN+ at 12:30 p.m. EST.
Köln manager Friedhelm Funkel - "The fact they missed out on their goal, automatic promotion, that can happen. But we do not need to assume that they are down. They will now be even more determined to make it happen."