It has a bunch of returning characters and hinges on the same full dive VR tech as its core, and that's pretty much it. It has the JSDF funding some research program into AI in a secret lab on I think it was an oil rig, where the scientists literally discovered the material form of the human soul and how to create artificial vessels for these, discover that they can copy their own literal souls into these machines except when powered on they immediately implode from the trauma of being locked in a void with no sensory feedback, and construct an elaborate virtual world to try to grow blank copies of literal human souls into sapient and complete artificial human consciousnesses, to use as disposable and infinitely replicable drone pilots.

That's the premise, at least: in practice it's a high fantasy adventure with a depowered amnesiac Kirito growing up and adventuring in a time-dilated artificial world while spy shit happens in the real world and an American PMC unit tries to steal the supposedly one complete artificial human soul (except the entire premise is flawed and tons of them pass the "Alicization" threshold without anyone noticing over the course of the story).

It's not a well written story and its core concept is not well thought out, it's just surprising in how decidedly it comes down on the "the residents of that artificial world are real people who should be treated with respect and accorded rights and self-determination instead of being tortured and exploited" theme.