Ainz Ooal Gown is acting like he is in a game, while slaughtering nations.
We are 4 seasons into Overlord and have yet to meet any other players. Is Ainz chasing a fantasy? Or are there really other players trapped there with him? Ainz doesn’t know, and neither do we the audience know either. That being said his goals since being isekai’ed into the game world have been murky at best. If anything the NPC’s are driving his actions more than he is. Ainz just happens to be the most powerful being, or the most powerful being we know of, due to happenstance. But what is it that Ainz is actually chasing?
Ainz believes he is still in the game, despite the NPCs (not just those in Nazarick) having seemingly their own lives and personalities. Not only do the NPCs have complex lives and relationships, they also have their own forms of governance and world order. That is until Ainz starts meddling in the world to learn more about the world around him.
That being said, Ainz is not really doing a good job of following any goals of his own, it’s not that he ever really had them. Ainz is the type of person who is along for the ride. If the creations of the floor bosses are any indication of how Ainz (or the Player Momonga) and his other fellow players in Nazarick were in relation to each other in the game, then we have to ask how did Momonga fit into the original Nazarick group? What was his place? He does not seem to be the natural born leader, or the cool one, but rather seems to be a groupie. An ally to support the genius plans of others, and occasionally give his own ideas to the group. And that is the same role he is filling as the leader of Nazarick.
Ainz has not grown since being isekai’ed.
While the rules of the world he is in have changed, he still acts like a player. The world is there for his own whims and amusement, rather than a serious place with living beings. He only cares about having fun with his Nazarick NPC crew, honoring the memories of his old relationships that are no longer. Ainz cared more about the game than anyone else, as evidenced by the fact that stayed on the game until the end. He was waiting, hoping that others would come back to the game before he ended up isekai’ed. And it seemed that besides one person who was curious, no one else came or cared.
In short Ainz was lonely, wanting to have friends more than anything else, wanting to once again be part of the legendary Nazarick crew.
But the Nazarick crew was only a memory, with only their creations left behind for Ainz to interact with. You think Ainz would have become concerned once the NPCs were no longer on the dialogue option and were capable of having their own thoughts and conversations. In a kind gesture Ainz decides that he wants the NPCs to grow as individuals and have their own personalities. He thinks the NPCs should be able to decide things for themselves. More than anything he wants them to be equals with him, rather than a master/servant relationship.
But fate is cruel to Ainz, who rather than trying to control and correct his NPCs from violence and delusions of power (which are becoming reality) rather lets the NPCs take their own actions. He doesn’t try to prevent hostile world takeover, and he doesn’t try to stem the violence. Rather he enables the violence in the pursuit of past memories of friendship. Ainz world perception dooms the people living in it.