 If you liked
.hack//Sign
|
 ...then you might like
Serial Experiments Lain
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Both are cyberpunk titles that have a similar protagonist who holds an intensely introspective and diffident persona. Both of these protagonists struggle with issues of identity in an online environment. Both are found trapped in cyberspace to a large extent. Both deal with a cyber-entity that is omniscient and holds questionable motives. Elements of .Hack//SIGN seem directly inspired by Lain and both incorporate an emotional bond between the protagonist and a special friend with even a brief scene touching on this in .Hack//SIGN which appears to be directly influenced by one of Lain's scenes.