The protagonist, a second-year student at Suimei Academy who barely visits school in the first place. He spends most of his time playing Empire Sweeper Online, in which he is the most famous and powerful player (known as Neidhart/Knighthart).
Artificial Human: Quite literally a figment of someone's imagination; In this case, that of the real Takumi Nishijou.
Classical Anti-Hero: He has intense social anxiety, isn't very brave, doesn't want to get involved, is frequently unpleasant and is rather judgmental. He's apparently intelligent, but prefers to spend all his time on meaningless hobbies. Nevertheless, he's the hero that Shibuya needs.
Fake Memories: Specifically, his life from the age of maybe 12 or so until starting high school.
Heroic BSOD: He has two during the course of the story. The first is after chapter 6, when he thinks his sister is dead. The second is after the revelation that he's an Artificial Human.
Hikikomori: Takumi spends most of his time in his own house (container on a roof). He does go to school once in a while, but he has managed to invent a chart which allows him to graduate with minimal attendance if he simply keeps following its schedule.
In-Series Nickname: Has three of them: Takkii, Taku and Takumi-shan. They are used respectively by Seira, Rimi and Kozue.
Jerkass: He's selfish, rude, self centered and has a lot of entitlement issues.
Mr. Imagination: Deconstructed. His detachment from reality goes up to the point where he could be diagnosed with schizophrenia.
Otaku: Takumi, having no interest in real-life world, spends a lot of his time immersed in games, anime and manga. He also possesses a collection of figurines.
Properly Paranoid: Yep, turns out Yua really did have ulterior motives in getting close to him, as should be obvious.
Split Personality: Takumi starts to think he had one that was responsible for the new gen killings. He was completely wrong.
Super Loser: He's a rude, selfish hikikomori with the power to make delusions real. Near the end he even embraces it and sneers at the adulation of the crowd after catching the killer. He's a loser through in through no matter how they want to look at him!
This Loser Is You: He seems to be the type that is written to be so pathetic so that anyone could feel superior to him.
Through the Eyes of Madness: He is a self-described disgusting, delusional, otaku, hikikomori who is approached by several beautiful girls all with a mysterious connection to a series of murders going on in Shibuya. This makes it extremely hard to tell where the events of the series lie on the line between paranoid hallucination and supernatural strangeness — if there is in fact any separation between the two at all.
Tomato in the Mirror: He's really a delusional existence created by Shogun, the real Takumi Nishijou.
A second-year student in Takumi's class, who claims to be Takumi's friend. She is a person who gives Takumi emotional support during the weird events that he has gotten into, despite the fact that he doesn't remember befriending her.
Affectionate Nickname: Rimi always calls Takumi "Taku." This is to differentiate between the two people she knows who call themselves "Takumi."
Cooldown Hug: Rimi delivers one to Takumi when he starts having a breakdown on a middle of a road.
Rose-Haired Sweetie: Rimi fits this trope surprisingly well. Aside from having the hair color, she also shows signs from all of the three personality traits (cheery, strong and sweet) that characters of this trope possess. She also gets bonus points from having a blue-haired love interest, Takumi.
Takumi's younger sister and a first-year student in Suimei Academy. Because Takumi lives on his own, she makes occasional visits to his apartment to check how he's doing.
Annoying Younger Sibling: Despite the fact that Nanami's visits to her brother's apartment and her occasional attempts to make him go outside (which sometimes work) are because of her concern about her brother's well-being, he firmly believes this to be the case.
Finger in the Mail: Happens when she gets kidnapped. Although instead of a finger, it's her whole hand.
Little Sister Heroine: Several 'Delusion' events play up this angle, such as with the indirect kiss scene.
A third-year student at Suimei Academy, who, after a warm introduction, is revealed to be following Takumi around. She's investigating New-Gen murders on her own for personal reasons.
Angsty Surviving Twin: Her twin sister Mia died in the "Group Dive," the first First Gen incident. Yua then launches her own investigation into Mia's death. She suspects Takumi is involved in the First Gen murders and pretends to befriend him under the ruse of being a girl otaku. When Takumi finds out her true intentions, she ... doesn't take it well.
Interrupted Suicide: Takumi's first conscious use of his delusionary abilities in the game is to create a flowerbed which breaks her fall after she attempts suicide by jumping off the roof of the school.
A mysterious figure who occasionally interacts with Takumi. He is shown to be an old man in a wheelchair. He is called "The General" in the anime's English dub. He is actually the real Takumi Nishijou, who is suffering from accelerated aging due to overuse of his powers. He therefore created our Takumi to take his place and do what he can no longer do himself.
Big Good: While he isn't a leader of an organization, he's still the primary force that opposes NOZOMI