When the first Xenos appeared 30 years ago, the Dungeon was surprised and so wanted to do more research. Thus the Colosseum where life and death occurred at very fast rate was created in order to pump out some Xenos. The safe area below the Colosseum is for where the Xenos born would escape to. But the experiment was a failure because this method wouldn’t produce a longing that is required for a Xenos to be born.
But an exception had occurred recently. When Fels and the Xenos went to the safe area below the Colosseum to build a Hidden Village there, they were attacked by a Xenos that fell from the wall above. The Xenos was so fast that it took the Xenos leaders and Fels to subdue it. Fels used a magic item to keep the Xenos frozen. The Xenos was the Juggernaut that fought Bell and Ryuu, and their fight caused the longing that enabled it to reincarnate. Its race is no longer a Juggernaut and its desire is to kill Bell. Fels think it should be killed because it’s too dangerous but Lyd said they could keep it sealed while finding a way to coexist with it. Bell was asked to decide what to do and he chooses to let it live. Bell will take care of the newcomer Xenos if the worst comes to it but he wants to find a way for them not to kill each other. The frozen Xenos feels a little irritated hearing it.
Other info include Lili and the others were on the trip too but they were left behind at the 20th floor because Hedin wanted to prioritize efficiency. Ottar trained at the 37th floor alone when he just became Lv4. Hedin wants a book from Ryuu’s hometown as a reward for the escort quest while Hogni wants to play a board game with Bell.