So there is a virtual reality device, the Nerve Gear, popularly used for MMOs.

As far as I'm concerned, we never see SAO or Alfheim using any sort of login screen.

Now, it makes sense for SAO to lack a login screen, since you can't log out. But what about Alfheim? How do normal, sane games authenticate their players?

  • Do MMO Nerve Gear games use username/password credentials?
    • Is it implied anywhere in the series? If I recall correctly, Kirito would just put on his Nerve Gear and instantly enter Alfheim without any sort of password screen.
  • Maybe the device serves as the credential itself?
    • But if I steal your device, I could impersonate you in all games...
    • Besides, using a device ID is not secure at all. If I figure out your device's ID, I could hack mine to use such ID and then login as yourself.
  • Perhaps they do some complex biological scan on your body to create an unique ID...
    • That doesn't sound very reliable. Or healthy.
  • 6
    Actually, I'm pretty sure there was a login screen, at the very beginning of the series, when he says "Link start!", you see a login screen and him inputting a username and a password. Mar 23, 2014 at 11:35
  • Yep, there was an account/password in the first episode.
    – Deathspike
    Mar 23, 2014 at 12:10
  • I don't know if I should comment or create a new question on this, but why would you need credentials if the gear is supposed to know who you are? Isn't the Nerve Gear almost equivalent to the best biometric interface ever? Yes, I realize there is a login and password in canon, but technology wise, after your body has been registered, wouldn't/shouldn't the Nerve Gear interface to the game recognize you when you hook up again?
    – SrJoven
    Aug 11, 2014 at 5:12
  • @SrJoven: The way software determines your identity, be it a by a login or some clever biological data, is called a credential. Also, the Nerve Gear is clearly flawed (the first version could kill people, and the second version can lower the pain limiters to the point it can cause physical damage), so we can't really assume it is as great as it seems.
    – Saturn
    Aug 17, 2014 at 22:29
  • @SrJoven: As for why using biometrics is flawed, consider being involved in some horrible accident: your biometrics could have been affected. Your general physical structure, your voice, or even your own mental status could have been modified. Now you can't login because your biometrics don't seem to match.
    – Saturn
    Aug 17, 2014 at 22:31

2 Answers 2


Your question can pretty much be answered by watching episode 1 of Sword Art Online.

The Nerve Gear uses a username and password identification system as shown at 01:37 of episode 1.

Account and password login screen

But as you mentioned, this does not occur in Alfheim Online. This is where we can consider the Nerve Gear to be the authentication factor, being a device that stores the save data.

We know it can save data Yui's data was saved to his Nerve Gear and was transferred to Alfheim Online as a result.

But if I steal your device, I could impersonate you in all games...

This would indeed be true, but doesn't the same count for login credentials? If you steal somebody's username and password, you can also impersonate that person in game. And don't forget, it's harder to steal physical objects all around the world than to steal some username and password from your home computer.

  • As a programmer, I've looked at authentication a lot. While its true that theft of a physical authentication factor means that you can be impersonated, it should be trivial to report that theft and get the permissions revoked. A perfect example would be credit cards. The first thing you do after you lose your wallet is call the banks to get new ones issued. Insurance would allow you to do the same with a physical device like a VR Interface.
    – ton.yeung
    Jan 11, 2015 at 10:17
  • 1
    Alfheim Online have a login system, but you cannot see it because isn't commented at novel or anime. You can know it because Asuna have two accounts (She reveals it at the end of Mother rosario arc). Feb 23, 2015 at 14:30

Extract from the light novel - Volume 3 Fairy Dance (ALfheim arc), p67-68

With that in mind, I put the NERvGear on my head and buckled the chin strap. With the frame in place and the goggles down, I closed my eyes.

Anxiety and excitement caused my heart to beat rapidly, as I tried to slow my racing heart beat, I said, “LINK START!”

The light passing through my closed eyelids suddenly disappeared. The transmission from my optic nerves was suddenly severed, and my eyes were enveloped by darkness.


At last, the final OK appeared, and the next instant brought me falling through the darkness into the colors of a rainbow, an illusion of the world. After passing through this series of rings, I had arrived in a different world.

-- Actually, it's still a little early to say that. Out of the darkness emerged an account registration interface. The main ALfheim Online LOGO gradually appeared, accompanied by a soft female voice.

Following the instructions given, I began creating my account and character. At chest height was a pale and shiny virtual keyboard and I entered a User ID and password as prompted. I had many years of experience before beginning SAO, so this process was of some familiarity to me. Since this is a downloadable MMO game, I would normally need to select the payment method, but I had bought this game and it came with a one month free trial.

Next I chose the nickname for my character. I didn’t put much thought into it, but entered the name «Kirito».

The ALfheim Arc in the anime doesn't show all the details.

Since Kazuto used the same login in both games - as you may know, ALfheim's database is a clone of SAO's one - he kept the same account.

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