If you're looking for anime similar to Chaos;HEAd, you might like these titles. All recommendations are made by Anime-Planet users like you!
For Kouta and Yuka, finding the bloody naked young girl on the beach would change their lives forever, for better or for worse. Unable to speak or function as a normal human being, she is named Nyu by the duo, and taken into their home in an effort to save her. But what neither teenager knows is that this innocent young girl is actually a killing machine -- an experiment gone terribly wrong -- and it is only a matter of time before the murderer in her awakens again...
Medusa is a mysterious illness which causes the body to petrify shortly after infection, found throughout the world and steadily increasing the death toll. In order to combat the disease, 160 lottery winners were chosen to be frozen until a cure could be found, one of whom is Kasumi - a twin whose sibling was not one of the chosen. Along with a group of others Kasumi awakens from her cryogenic chamber, but not to the same world she left it: prehistoric monsters roam the now-abandoned castle and eat the survivors, while endless giant thorns rise all around them. Against all odds, Kasumi and the others must now try to survive the horror of their situation and discover the truth behind what's happening, all the while waiting for the Medusa to finally claim their lives...
In a massive online world, people act only as well as their conscience demands. When one player's punishment is to be trapped in this world, a disparate group of people seek the answers why. Their motives are varied; their methods even more so. What stands between when we tear down the walls of reality? Where does our soul end and we begin?
This is sort of a weird recommendation - Chaos;HEAd deals a lot with delusions but it happens in the "real" world, while .hack//SIGN happens in a MMORPG (ironically called "The World"), so their settings do set these shows apart.
With that said, Chaos;HEAd has a ton of ideas and terminology that relates back to the digital world, with characters wielding "Di-Swords," and other references to computers and games. While Chaos;HEAd has a plot that some say might is overloaded with ideas, if you liked some of the ideas involving mysteries and delusions presented in Chaos;HEAd, I'd suggest checking out .hack//SIGN.
Japan has reclaimed its former glory under the guidance of Kings, charismatic individuals wielding incredible powers. But now, one of the Red King's vassals has been murdered, and a viral video shows the killer's confession at the scene. He is one Yashiro Isana, claiming to be the Colorless King; and he is now a wanted man - not only to the Red King's faction, but also the Blues charged with keeping the peace. He is even sought by Kuroh Yatogami, a knight of the former Colorless King sworn to slay any unworthy successor. Only, the subject of their struggle, "Shiro", is a nondescript young man living an unremarkable life in an island academy, and seems to have no recollection of killing anyone. To keep his life, Shiro must prove his innocence; but what is the truth behind his mysterious past, and what will be the outcome of this confrontation of Kings?
Honestly, I'm surprised that I'm the first person to make this recommendation. From the first episode of K, I immediately thought of Chaos;HEAd. Both anime have a weird sense of disconnect that makes you question the reliability of the main character. The worlds the main characters live in are somewhat similar as well, where things are not as they seem, with superhuman powers and murders abounding. Both have impressive animation and voice acting to boot.