Inside the grand tower on one of the Amra planets, for a long time the Blades had struggled to get past the 50th floor. It was a central point in the tower and many struggled to do so as well.
This was because the floor was more of a testing floor, one would have to beat a special evolved type of Amra to pass. They didn't need to kill them, but just be strong enough to allow them to reach the next stage.
This stage could also be done with as many people as one wished. They had to go against five Amra at the same time. Due to the nature of the test as well, only one group, however small or large, could take the 50th floor at the same time.
The 49th floor had a large living area that would allow one to rest and buy supplies and more before they went to the 50th floor. On top of that, whatever floor one went up to, they could use the teleporters located at each floor to quickly transport between them.