The following contains spoilers for DanMachi season 3, available on HiDIVE
At the end of Ghost in the Shell Innocence, the Major sums up the totality of the events with a parable: "We are saddened by a bird's cry but not a fish's blood. Blessed are those with voices." In Is It Wrong to Try to Pick Up Girls In A Dungeon season 3, the emergence of an intelligent monster species turned the entire show on its head, and the repercussions are still felt going into the currently airing season 4. At the beginning of season 3, Bell Cranel finds a young Vouivre, a humanoid dragon creature that speaks, and soon befriends her, naming her Wiene. Soon after, it's discovered that an entire subset of monsters is capable of speech and higher intelligence and that they've existed for a long time, known as the Xenos.
But how exactly did the Xenos come to be, and how has their existence been kept so secret? Additionally, what goes do they have in life? Revenge against adventurers who have killed them indiscriminately from other monsters? Or maybe something more?
A Fresh Start
The Xenos are actually monsters that have reincarnated after being killed by adventurers in previous lives, possessing memories of when they were cut down. Just like adventurers, they too fight the less intelligent monsters, who attack Xenos like anyone else, as if the price of intelligence is being preyed upon.
It is by killing regular monsters that the Xenos become stronger through the consumption of the gems that monsters drop. They've no need for the monetary gain that the gems provide to adventurers, opting to level up more directly. It's for this reason that Xenos can be considerably tougher than typical beasts dwelling in the depths.
Not all Xenos are capable of speech, but they all tend to band together, forming a tight-knit community that hides within the dungeon. Having been born inside the dungeon, the Xenos see it as a maternal entity and the occasional hideaway as a blessing. However, even with those havens, they yearn to leave.
The Mission of the Xenos
Once Bell and the Hestia Familia are made aware of the existence of the Xenos and spend some time with them, they are told their dream: to live on the surface, without fear of being hunted. Obviously, given the fear of monsters and the secrecy of Xenos' existence, such a dream is difficult to foresee coming to fruition.
However, they aren't without support on the surface, as Ouranos, the god at the head of the guild, and his loyal mage companion Fels, have been aware of their existence. At first, the prospect of the head of the guild helping the Xenos seems outlandish, as the Guild is sending adventurers down to hunt monsters.
However, it is made clear that Ouranos does what he can to support and protect the Xenos from being targeted. The Hestia Familia's intervention in affairs is seen as a blessing that could hopefully make the Xenos' dream come true. But it isn't without hardship.
Season 3's Conflict
The existence of Xenos' may be secret, but it hasn't prevented those who know of their existence from exploiting them, capturing them, and using magic to bind them to their will. Such intentions are displayed in season 3's latter half when the Ikelos family attempted to kidnap several of them. In the ensuing chaos that spilled onto the surface, Bell nearly sullied his reputation by protecting a mindless, rampaging Wiene.
Even after successfully helping the Xenos escape back down to the dungeon, Bell only salvaged his reputation by fighting another Xenos, the Minotaur Asterius, the reincarnation of the Minotaur Bell killed in season 1. In the end, the Xenos were safe, but no closer to achieving their dream.
Not all Xenos are interested in the surface, as Asterius only cares about fighting Bell, but regardless, the plight of the Xenos continues to be one of this series' most compelling aspects. Ouranos and Fels put their faith in Bell, hoping that as he continues to conquer larger and larger obstacles, he can also push the city of Orario towards accepting the Xenos on the surface.