Back in middle school, Yuuta was himself a victim of "Chuunibyou Syndrome", fancying himself as the "Dark Flame Master", a goth guy clad in black who can wield dark-purple flames. Nowadays, though, he'd rather disassociate himself from it, which caused him to become stigmatized, thus come high school he moves away far enough to where his old classmates cannot find him. But his past still comes back to haunt him, one way or another, when he meets a girl still suffering from chuunibyou... who proceeds to blow his cover.
All the Other Reindeer/Eating Lunch Alone: The direct consequences of his overblown middle-school fantasies. Thus he considers Makoto's offer to eat lunch with him as a good start to a far more normal high school life.
Bandage Dude: Used to wrap his arms as part of his "Dark Flame Master" persona.
Chekhov's Gun: Yuuta's collection of items related to his "Dark Flame Master" persona, which he originally planned on throwing away come tenth-grade, turn out to be useful whenever he has to distract and/or keep Rikka and Sanae preoccupied.
Cloudcuckoolander: Used to be one during his "Dark Flame Master" days, going so far as to, in Lite Episode 3, bring an unconcealed rifle out in public while accompanying Kuzuha's friend (but at least he's sensible to hide it in the presence of a cop).
I Just Want to Be Normal: Sincerely hopes to leave behind his middle-school weirdness behind and spend his high school days in relative normalcy, by transferring to a high school far enough that no one from his old school would attend. He accomplishes that for the most part, but then came Rikka.
A strange girl who wears a medical eyepatch over her right eye and has just moved into Yuuta's apartment building upstairs with her older sister Touka. Unlike Yuuta, Rikka indulges in her delusions even well into high school in the form of "The Wicked Eye", a goth-loli who wields a weaponized umbrella.
Adorkable: As a result of her small and cuddly appearance awkwardly contrasting with her delusions of grandeur.
Gets broken again at the end of episode 10 where the last support she has for her delusions, Yuuta, suddenly turns on her and tries to make her face reality right before they were supposed to perform at the school festival and not even a day after they had confessed to each other.
Cloudcuckoolander: Looks at the world through the lens of her fantasies in a near-constant basis.
Everybody Hates Mathematics: Rikka is frankly terrible at it. While she lucks out in the anime due to the class average being lower than usual, in the light novels she has to retake the exams at least thrice, and passes none, with her highest being 30/100.
A beautiful, chuunibyou-hating girl in Yuuta's class who is also a transferee. In the anime, her attitude is explained as the result of her desperate attempts to erase all traces of her past as a chuunibyou herself, having went by the name "Mori Summer", a medium and writer of the "Mabinogion", her journal of faux-philosophical rants currently in Sanae's possession.
Alternate Character Reading: The kanji of her given name can also be read as "mori natsu" ("forest summer"), thus her chuunibyou alias "Mori Summer" in the anime. The light novel version of Mori-samajust took the first kanji.
Berserk Button: Any mention of chuunibyou, given her past as one, as well as (in the anime) Sanae's insult to her as a "Fake Mori Summer".
Bitch in Sheep's Clothing: She's not exactly a bad girl at heart, but she can get pretty snippy and mean every time the issue of chuunibyou is taken up because she's just that desperate to erase all traces of her own past as one.
The Bully: Towards anyone she regards as her moral inferiors.
Old Shame: In-Universe — like Yuuta, Shinka resents her past life as "Mori Summer". Unlike him, however, she's not as good as him when it comes to facing the fact that her past will always haunt her.
Really 716 Years Old: Claims her "Mori Summer" persona to be this, as well as the "oldest mage in the world".
Red Baron: Mori Summer in the anime, and Mori-sama in the novels.
School Idol: Downplayed. She is without dispute the class idol, but nothing was mentioned beyond class 1-4.
Shaggy Dog Story: No matter how hard she tries to purge it, "Mori Summer" will always live on in Sanae's delusions. And to add insult to injury, Sanae won't even acknowledge Shinka as the real deal because she doesn't match up to her "Mori Summer" image.
Anime-exclusive character. A sweet kid and Yuuta's upperclassman who's quick to fall asleep.
Alternate Character Reading: The kanji for her surname is written as "五月七日" (May 7) — Tsuyuri being a festival that falls on that day. In Episode 2, Yuuta did mispronunce that as "Gogatsu-nanoka", and has to be corrected.
Anime-exclusive character. A kid from the school's middle-grade department. Like Rikka, whom she met on the internet, Sanae also suffers from chuunibyou. She takes on the form of "Mjolnir Maul", a mid-range fighter who uses her long bola-resembling twintails to fight - which more often than not serve as hindrance rather than help. In the world of delusions, she then "switches over" to a gigantic hammer.
Badass Adorable: Like Rikka, the "badass" part is debatable, the "adorable" part undeniable.
Expecting Someone Taller: Refuses to acknowledge Shinka as the girl behind "Mori Summer" because the former was expecting the messenger of love, not the jaded high-schooler desperate to purge her past delusions.
Verbal Tic: Vocalizes the word "desu" to sound like "death"note Japanese can't really pronounce the ending "th," so they vocalize that as "s." The difference between "desu" and "death," is more that of a tone..
She changes to "desu yo" after Yuuta brutally lectures her on reality.
Butt Monkey: While most of the main characters are unlucky, Isshiki is arguably the unluckiest. For example, the poor fellow's attempts at wooing Kumin with the later never noticing one bit. Even better, when he finally does confess in episode 10, it's on a stage in front of the entire school, unfortunately she was asleep at the time.
While Yuuta will give the girls a smack or chop every so often, when it comes to Isshiki, he pulls out all the stops and just wails on him. It comes to a peak at episode 10, where the poor guy gets kicked in the face, his head slammed into the floor multiple times, and comboed.
Important Haircut/Traumatic Haircut: He promised to shave his head bald as gesture of apology to Class 1-4 when his girl-ranking book was discovered. Turns out he doesn't want to go through with it, but is pestered by Shinka about his vow. Poor guy isn't happy at all, especially considering he had to deal with being bald for the past three years, and fears he will end up Prematurely Bald like his father.
Smarter Than You Look: Of course, being a teacher, she's intelligent, but Yuuta notes that she can be quite cunning, as shown when she plays along with Rikka's delusions while the latter submitted her club formation form for her "Eastern Magical Nap Association".
Anime-exclusive character. Rikka's older sister and a professional cook, with whom she has a not-so-good relationship, owing to the fact that she mostly serves as the serious foil to her insane antics.
Arguably a Deconstruction. Her aloofness results from her inability to handle her sister very well and her own emotional problems. As a result, she ends up hurting her sister more than helping when it comes to her time of need. Even she realizes this herself, and often asks Yuuta for help.
Establishing Character Moment: Her first conversation with Yuuta, she described Rikka's delusions as problematic, forced her to get rid of the cat (to be fair, she has allergies) and blackmails Yuuta into taking care of it.
Jerk with a Heart of Gold: She's abrasive, rude, cynical, and hurtful, but she really does have good intentions. She tries to help her sister, just not in the nicest ways.
Knight of Cerebus: A non-villainous example. Despite being Comically Serious, her arrival is often a sign that things are going to become sadder, as she tries repeatedly to bring Rikka back into reality, however harsh it may be.
Supreme Chef: Rikka may not like Touka much, but at least she appreciates her cooking.
In episode 10, it was revealed she would be sent to "the head restaurant in Italy" for training.
Light novel-exclusive character. Yuuta's chuuni friend from middle school who suddenly moved away. Yuuta mentions that she's probably the reason be got infected with chuunibyou. Unlike Yuuta and Shinka, who have been cured from chuunibyou, and Rikka, who is infected but is unaware that she has the disease, Satone is completely aware that she is infected and is loving every moment of it.Her chuuni persona is Sofia Ring SP Saturn the 7th, or Sofia-chan, the Magical Demon Duchess.
Murder the Hypotenuse: Kidnaps Rikka and makes Yuuta play a game with her where they have to break up if she wins.
New Transfer Student: She transfers in to Yuuta and Rikka's school and class at the end of the second novel so that she can fight against Rikka, over various things.
Rose-Haired Girl: Her hair is a shocking bright pink. Particularly jarring, given how realistic the color palette used for the art in the light novels are (where even Rikka's dark blue hair can be seen as a stylized black).