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Yamabuki High School's arts program attracts students from all around the country. The Hidamari Apartments is a small apartment block across from Yamabuki High School, infamous for housing weirdos from the arts program. But they've all graduated! We're normal now!
—Customary introduction to the Hidamari Apartments at every year's welcoming party
Hidamari Sketch is a Slice of Lifemanga and anime series centering on a young girl named Yuno who is accepted into the Yamabuki High art school and moves into a small apartment building nearby. She makes friends with other girls living in the building, and cute things happen.Animated in early 2007 by Studio Shaft, based on a 4koma in Manga Time Kirara Carat by Ume Aoki, this series is best known for its slow pacing, focus on artistically inclined characters, and diabetes-inducing levels of cuteness. A second season, Hidamari Sketch x 365, aired about a year after the first, and a third, Hidamari Sketch x ☆☆☆ ("Hoshimittsu"), was aired in the Winter 2010 season. A fourth season, Hidamari Sketch x Honeycomb, began airing in October 2012. Each season (except Honeycomb) has two extra Original Video Animation episodes, and there are two independent OVAs as well, Hidamari Sketch x SP (released in Fall 2011) and Hidamari Sketch Sae Hiro Sotsugyou-hen (released in Fall 2013).The manga is licensed by Yen Press under the title Sunshine Sketch, and the anime is licensed by Sentai Filmworks under the original name in a subtitled-only release.
Hidamari Sketch contains examples of:
Accidental Pun - Sae's embroidered poetry journal — Shishuu is a homonym for both "poetry collection" and "embroidery".
Adaptation Expansion - Both Hidamari Sketch and Lucky Star started serialization in early 2004 and were animated in early 2007. But the former is slow — as in about fifteen strips on the same story arc per month — while the latter goes much faster and story arcs are seldom longer than two strips. So why does Hidamari Sketch have 42 episodes of anime, the longest of any modern moe-style yonkoma as of this writing? Because Studio Shaft have inserted a large amount of content in the three anime seasons produced to date, most significantly:
The introduction of Chika, Sae's 13-year-old sister, who was unnamed and only referred to in the manga.
Episode 10 of Hoshimittsu, in which Yuno flushes her keys and has to bunk with all other Hidamari tenants for several nights in a row, was significantly expanded from the manga version, in which only one night with Miyako is drawn out — but the landlady still takes 5 days to find the keys, according to one title — while the anime portrays Yuno's stay with every other tenant.
Affair Hair - The incident described in Sprouting Ears, below, occurred because Yuno's father found a strand of hair (the same colour as Sae's) in Yuno's room, which he construed to mean that Yuno had slept with Sae.
Anachronic Order - Even though it's a simple Slice of Life series, the first three seasons' episodes don't take place in chronological order. Luckily, each episode gives a calendar date in its title, and the manga and Honeycomb are somewhat in order.
Art Shift - Cleverly done in numerous scenes. In the love letter episode, Yuno has an Imagine Spot during an art history class, the imagined scene imitating the art styles of Fauvism and Cubism. A shift to watercolor style is used several times for particularly emotional scenes (Sae's moment of closeness with Chika after she passes her exams, Yuno's sadness when the stray cat they adopted runs away, etc). Numerous other brief art shifts are employed too, from cut-out silhouettes to black-and-white marker pen-style drawings.
Ascended Extra - Chika, Sae's younger sister. She was only referred to in the manga and hadn't even been named, but her role was greatly expanded in the anime, especially in 365.
Badass Grandpa / Cool Old Guy - Despite appearances, the Principal is shown to possess lightning speed and reflexes, ninja stealth, and the physical prowess needed to jump the school gate and adjacent street.
The Gates question becomes even more entertaining once you realize that Nori's computer looks almost identical to an Xbox 360.
In the second episode of Sotsugyou-hen, the Landlady was seen drinking Umesu beer.
Nori order's pizza from Domiso's
Blank White Eyes - Yuno does that all the time; while Hiro does that when the paranormal is involved.
Boarding School - Strange variation. Yamabuki is certainly not one, but as discussed in the page quote, the main characters came from different places around the country so they need to rent apartments — and Hidamari Apartments, our point of focus, is one of them.
Breathe on the Fan - Yuno and Miyako catch Sae talking into the fan, pretending to be an alien.
Brick Joke: Nazuna attempts a drawing and the characters spend a few strips trying to guess who it is. It isn't until a few chapters later that it's revealed to be the landlady.
Call Back - Honeycomb episode 9 is full of them, starting with three in Yuno's dream right at the very beginning.
Chalk Outline - Played with. Miyako drew a chalk outline of Hiro at where she passed out, despite Sae's objection over taste. Sae ended up envying Miyako though, as Miyako drew the outline in the style of Amedeo Modigliani...
Chocolate of Romance: In the anime adaptation, Sae received Valentine's Day chocolates from girls when she was in junior high.
Class Trip - Quite commonly used as the art students goes out in the neighborhood to sketch sometimes.
In Honeycomb (and manga volume 6), Hiro and Sae went to a more traditional Japanese school trip to Hokkaido.
Cloudcuckoolander - Miyako is sometimes like this, while Yoshinoya practically lives there. Yuno drifts into this territory on occasion when exposed to puppies and paintbrushes, and Misato (the previous tenant of 101) was portrayed like this in Episode 9 of Hoshimittsu.
Color-Coded Characters - And symbol coded as well: Yuno's X-shaped hairpins; Miyako's cat-paw mark on her stomach (which was an effect of a cat falling asleep on her while she was sunbathing); Sae's glasses; Hiro's tentacle-hair-accented hair buns; Nori's computer mouse (she's the only tenant that can use a computer — Japan's heavy use of mobile services means few people actually bother to learn using PCs); and Nazuna's jiggly headbands.
Color Failure - Sae and Hiro, when Yuno and Miyako first mentioned that Yoshinoya is their teacher. Nori and Nazuna also exhibit this, after hearing about Yoshinoya's childish antics for the first time.
Coming-of-Age Story - The main premise of this story, if not particularly clear to some, is of Yuno's wanting to become mature. This is kind-of lampshaded whenever she's shown to be overjoyed by any suggestion that she's matured, even a little bit.
Continuity Cavalcade - In episode 9 of Honeycomb, the Hidamari residents try to remake the Game Of Life to better suit them — it's not as if art students will eventually become doctors — which ends up replacing life events in the game with events from the story. Some of their discussion are also continuity nods. An incomplete list follows.
Yuno and Hiro mention their experience painting Hidamari's sign and comment that it "seems like so long ago." This comment is particularly true for viewers and readers, as the content in question was published more than half a decade ago.
After Nazuna explained why her miso soup has too much tofu (the tofu in her fridge is close to expiration), Miyako mentioned the "Tofu goesnote i.e. spoils fast" gag. Nori and Nazuna's response were the same as what Miyako thought in Volume 1, thinking a running piece of tofu.
"Entrance Ceremony and Welcoming Party" — see quote at top.
The incident involving the "Yamabuki-jizou," partly mentioned at the first example of Schoolgirl Lesbians, below.
"Crab Fried Rice" — this was animated in Hoshimittsu.
"Win the blessings of the Northern Seas" — Miyako's winning of a newspaper crosswords in X365.
The episode starts with Yuno dreaming about playing in snow with Miyako, as she did very first episode of the anime — but this time homophones don't trip Miyako up.
Continuity Nod: In episode 10B of Honeycomb, the girls held another hyoza party for Chika again... And like last time (in X365), there were also candy-shaped gyoza.
Corner of Woe - The Four Girl Ensemble was having a chankonabe — sumo wrestler's hot pot — prepared mainly by the weight-conscious cook Hiro. And then Miyako and Sae (probably) incidentally uttered lines usually reserved for sumo wrestlers, which prompted Hiro herself to leave her apartment and sit in the Corner of Woe in the backyard.
Yuno almost walked off into a garbage pile of woe in one chapter upon discovering that someone she thought as more talented than her was forced to leave school while she was still there. The anime handled this scene somewhat differently, by only giving Yuno a spotlight.
Couch Gag - A relatively subtle one; in the opening of 365 Miyako is shown eating a different dish in each episode (video). The scroll on the wall behind her also changes each time. The message Hiro writes on the paper plane sometimes changes from the normal "ayafu~ya roketto" too, though not in every episode.
The beginning of Honeycomb's opening has 3 stills that always change with each episode.
Cram School - The series discussed the existence of a type of cram school for art-stream high school students that wanted to continue doing art in college, called research institutes. In fact, Arisawa's rendezvous with Yuno was related to this; she skipped Institute class that night because of the pressure and stayed at school to paint, and answered Yuno's cell phone when it was accidentally left behind. Institutes are, in fact, Truth in Television.
Cultural Cross-Reference - Miyako likes to invoke strange English references, especially in the anime. Even in manga, she discussed the The Gift of the Magi in the "Polaroidzilla" story — to the puzzlement of her very Japanese co-tenants.
Curtains Match the Window - With the exception of the Principal who is Eyes Always Shut, all characters are like that: Yuno is brown, Miyako is yellow, Sae is blue, Hiro is pink, Yoshinoya is green, and the landlady is brown, Chika is light purple, Natsume is blue-green, Nori is blue gray and Nazuna is blond.
Ear Cleaning - When Hiro, Miyako, and Yuno walk in on Sae's room and find her asleep on the floor with a note on the progress of the story she's writing, Hiro kneels down and puts Sae's head on her lap. Yuno, charmed at Hiro and Sae's intimacy, runs over and offers Hiro an ear pick, to Hiro's confusion.
Early-Bird Cameo - The two new tenants of the Hidamari Apartments, Nori and Nazuna, were de-faceless masses-ized among other admission exam takers in the second 365 special episode.
First Name Basis - Subverted; Miyako was just being a Genki Girl when she asked Yuno to call her on a first-name basis, and settled on Yuno's nickname.
That being said, all of the nonadult characters are referred to by their first names only (we don't even know what their last names are), meaning that this trope has been in effect for all the girls from the first time we see them.
Five More Minutes: Honeycomb starts with a scene like that, by Yuno. This also mirrors the start of manga volume 2.
Furo Scene - Once an Episode the viewers get to see Yuno reflecting on the show's events in the bath. The main cast also once attended a public bath together, which is typically used for the purpose of comedy and not so much for Fanservice.
Generic Cuteness - Hiro worries a lot about her weight, but any differences in body frame she may have aren't really that noticeable. On the other end, Sae is supposed to be tall. Yuno is still adorable, though.
Goofy Print Underwear - Yuno was deeply embarrassed when a locker room prank exposed her kitten-print underwear. To be fair, she doesn't wear those every day, but still...
Gratuitous English - Miyako spells out "LOVE AND PIECE" in the snow and gets corrected later by Hiro; she also likes peppering her speech with English, even up to Mother Goose references. See also Motifs, below. The labels are usually right, except... "Hidamari Sckech"?
When Miyako pranks Sae by putting stuffed animals in her futon to make it look like a stranger is in there, Sae, who thought the "stranger" must be a foreigner as the shoes were put next to the futon, asks, "Who are you?!" when she first sees it. Hilarity Ensues.
To prepare for a make-up exam, Miyako has Yuno name almost everything she sees in English. Yuno continues the habit long after she takes (and passes) the test. During lunch, Miyako asks Yuno to name items which don't have a direct English translation.
Growing Up Sucks: After the girls start watching part of the new version of Lovely Chocolat, their old favorite TV show, Sae notes that they're still watching it even though they're in high school. (and are therefore supposed to be out of the Fleeting Demographic). Upon hearing this, Hiro's hair falls flat, and she laments about how growing up is no fun. This also becomes a plot point in the manga and later anime specials, due to a lack of Comic-Book Time, which means that Sae and Hiro eventually graduate and move out.
Exemplified even more when the trope causes Hiro to fall into a Heroic BSOD when she laments how she'll be leaving everyone at Hidamari behind after graduating.
Harsh Word Impact - Done with speech bubbles in the manga and arrows (the graphical symbol, not the projectile shot from a bow) in the anime.
How We Got Here - Sotsugyou-hen is structured like this. Yuno woke up early in the beginning of the two-episode special on the day of Sae and Hiro's graduation ceremony, then spent the rest of the first episode recalling Sae and Hiro's college entrance exams and decisions which spent most of the month previous. The graduation ceremony proper is in the second episode.
Huge Schoolgirl - The opening of the first anime season has the girls running together and Miyako is the tallest of the bunch, beating even the willowy Sae by a small margin. This is seldom addressed in any version, though, except in comparison with Yuno who is at the other extreme.
Once in the anime she mentioned she serves jellies used as meal substitutes with sweetened condensed milk.
In the first episode in Sotsugyou-hen, she complained to her underclassmen about gaining 3kg during her college entrance exams as her underclassmen all made her tonkatsu for lunch. Then Sae enters with cake... No guess what happens.
Also in the first episode of Sotsugyou-hen, the tenents serves two pizzas to celebrate for Hiro getting into her first-choice college. Hiro said she doesn't have much appetite because she's still nervous... Then proceeded to stuff her face with two pieces of pizza.
For Honeycomb's, the main characters get paired off for duets. Chika gets in on the fun by having one with Sae. The last one is a group song with the tenants sans Hiro and Sae with quite a new musical nods to the openings.
Indirect Kiss - Natsume was certainly thrilled to receive Sae's leftover sandwich.
Lovable Sex Maniac - Yoshinoya, in the manga. She's able to suggest going nude at the drop of a hat, and comments that Yuno's small butt looks cute. Understandably, most such references did not make it to the anime.
Some of the things that did make it into the anime involved one scene with Yoshinoya-sensei deciding to go Hadaka Apron style — which usually involves a girl wearing an apron and nothing else (although she did wear a small bikini underneath it) — after seeing another class in the middle of cooking.
And then there's the time when Hiro — walking home from shopping — encounters a smiling Yoshinoya in a heavy trenchcoat in the middle of summer. Just as Hiro finishes asking her what she's doing, Yoshinoya flings open her trenchcoat and appears to flash Hiro, causing her to drop her bag out of shock. (As revealed a moment later, Yoshinoya had been wearing a new swimsuit underneath, and that's what she had wanted to show off.)
Measuring Day - Volume 4 has an entire chapter on this. If even Yuno skipped breakfast for the day, it's not hard to guess what Hiro did...
Motifs - The show combines a variety of abstract visuals such as half-tone patterns, photographs, and labels to make the show seem like it's made out of a collage, which matches the characters' interests perfectly.
Colored backgrounds patterned with simple two-dimensional shapes and especially a half-tone relief pattern◊ are commonly used in place of realistic backgrounds or solid colors. They're used when the show is illustrating something abstractly. In addition, objects being talked about or used by a character are often abruptly shown on one of these backgrounds.
Photographs of real objects are spliced in seamlessly with animated objects. For example, Yuno's alarm clock and teddy bear are both depicted using photographs.
Objects or groups of objects are individually labeled in English. For example, a tea set is shown and each teacup is labeled "teacup".
The colors of the mailboxes outside the apartment are almost never the same, sometimes changing in the same scene. In an episode where Yuno stays home sick, the mailboxes each show the body temperature of their tenant◊ with Yuno's mailbox being a different color from the others.
Each character has a "symbol". Yuno's is her 'X' shaped hair clips, Sae's is her glasses, Hiro's is her spikey odango hair, Miyako's is the cat-paw shaped tan line she got when she slept on the roof with a cat on her belly, Nori's is a computer mouse as the only PC-user among the tenents, and Nazuna is her hair band. The characters' actions are often illustrated abstractly by showing their symbols on a patterned background. For example, Yuno's symbol is shown wobbling forward to illustrate her walking over to her friends.
There was one strip when Yuno entered a gift shop and found some of the animal toys fitting her co-tenents: for Hiro, a sheep; for Sae, a black cat, and for Miyako... a dancing flower.
Chika does something similar in Hoshimittsu episode 7; designating Yuno a hamster, Miyako a cat, Hiro a swallow, and Sae a gecko.
Mood Whiplash: The comedic focus makes the scenes where things get more serious, like Yuno wondering about a piece of art in the garbage or Hiro stressing out about having to graduate someday, stand out.
There's also an incident in Volume 4 of the manga (and Episode 3 of Hoshimittsu) where she describes the electives for the Junior class where she describes the electives (2D, 3D and digital arts) while framing variousbody parts with her hands in a suggestive fashion and inviting the students to 'touch them once they'd made their selection'.
Mysterious Past - There are lots of rumors about Yoshinoya-sensei's past and the little information she gives just adds to the mystery.
Miyako also has one of her own, as she occasionally drops comments about having to navigate using the stars along with an incident involving a lack of lifeboats and having to learn to swim quickly. She also drops hints about her family history, including singing in bars and inheriting her brothers' toys.
Mythology Gag - The anime openings (at least x365's) make reference to scenes in the manga that never make it into the anime, such as Yuno's 4koma-robot and camouflage Santa. They even put in some frames that had just gone to press. See also Bait-and-Switch Credits.
New Technology Is Evil - Nori thinks Sae has this attitude when the two discuss old-style dictionaries vs. computer notebooks to stay organized.
Noodle Incident - Miyako is riddled with bizarre mysteries. Evidently, she had to rely on the stars for guidance at some point, and arrived at Hidamari with all her belongings in a two wheeled cart.
Misato's graduation project shut down the girls' bathroom for two weeks.
Not What It Looks Like - The second season has Yuno walking in on Sae posed on all fours over Hiro and starts freaking out. Turns out the two were practicing for the school play, with Sae being the criminal. Oddly, this scene is depicted in the OP for the first season, making it Bait-and-Switch Credits at the time.
Two examples of this appeared in the same chapter in manga volume 4, all related to Yoshinoya. At first, she invited Miyako to the art preparation room to properly fix the tear in her uniform, but she declared to the whole class "I'll have you strip there, and you can leave the rest to me. I'll take care of it nice and quick. (heart)" And the next day, when Yoshinoya came again... "Yuno, you... forgot something... (heart)" while holding up her missing uniform ribbon. Certainly the other students got the wrong idea. The anime fudged it a little, as Yuno is shown wearing the ribbon in a few scenes between leaving the art prep room and the following day.
Ocular Gushers - Sae has a pretty pic one in the first episode of Sotsugyou-hen, when Hiro got into her first-choice college.
Odango Hair - Hiro. She was annoyed that she couldn't braid her hair into these when it's humid, and Miyako once saw Hiro's odango as cream puffs in one episode, when Hiro's class was making cream puffs in the home economics class.
Once an Episode - Yuno waking up to shut off her alarm clock, the Disturbed Doves in front of the school, the girls eating together, and Yuno taking a bath at the end of the day, with a cut showing the dropping of a bath bomb into the water. Hoshimittsu replaces Yuno waking up with some Yoshinoya antics and having the girls do morning exercises.
Sometimes some of these scenes appeared in an ridiculous way. In the first episode of Honeycomb, the ending Furo Scene switched to the hot springs where the twelfth-graders were lodged. There's still a cut of a bath bomb being dropped into the bath water, despite the fact that nobody would ever drop a bath bomb in a hot spring...
One Head Taller - Subverted. Miyako is much taller than Yuno, and Miyako did tuck Yuno under her chin quite often, but those incidents were never romantic in nature.
"On the Next Episode of..." Catch Phrase - "We'll be waiting at the Hidamari Apartments, please come and watch!" (On occasion Yamibuki High School is used instead of Hidamari Apartments, in accordance of next episode's content.)
Origins Chapter - The last chapter of Volume 4 was used to explain why Natsume was such a Tsundere towards Sae. It is also one of the few chapters not drawn in yonkoma format.
To a lesser extent, Yuno's parents. They can be a little oddball and embarassing, but did at least worry about their daughter's decision to live alone. Her dad is also the classic Overprotective Dad, so they haven't completely abandoned their parental roles, even if they do like to recapture their youth by visiting amusement parks.
Photo Montage - Several episodes (including a special that actually featured the characters playing with a Polaroid camera) feature photo montages over spoken conversation.
Placeholder Titles - Studio Shaft was again unable to meet the deadline for Hoshimitsu's OP, so for the first 2 episodes it was just a very simple one with a lot of stars. The finished version first appeared at episode three. The ED remained similarly incomplete until episode four.
Puni Plush - The characters look very young for their supposed age, especially in the nude.
Quirky Household - As mentioned in the page quote, the Hidamari Apartments long has such a reputation.
Right Behind Me - Whenever Miss Yoshinoya says or does something inappropriate, almost invariably the principal appears behind her and drags her away to reprimand her. This happens so often that she eventually becomes paranoid and whirls around to check behind her after she suggests going to a restaurant instead of a staff meeting. Cue the Principal's Sneeze Cut.
Romantic Two-Girl Friendship - Sae and Hiro, very frequently the subject of Ship Tease. Hiro talks about giving Sae chocolate for Valentine's Day and how Sae watched over her all night when she was sick; the OP even has the Not What It Looks Like moment with Yuno walking in on them (with the context not even being given until the second season). Sae spends an entire episode (the 2nd special) freaking out when Hiro gets a love letter in her shoe locker, complete with an excited Yuno and Miyako misunderstanding the letter as coming from Sae. And then there's the second season's opening...
Yuno and Miyako also have their moments, which usually are attributed to Miyako's extreme bubbliness and careless attitude toward nudity or physical closeness in general. Miyako also appears to be very open-minded about relationships (see Schoolgirl Lesbians) and hops in the bathtub with Yuno the day they meet, since her own water supply doesn't work. One time Miyako even tells Yuno that she thinks she is very pretty◊. Yuno in turn voices her wish to Miyako that they might one day have the same relationship as Sae and Hiro.
Same Clothes, Different Year - Yuno's parents showed a photo of her from kindergarten and she has the same crisscrossed Bobby pins in her hair.
School Festival - Being in an arts class meant the Bunkasai is really cultural. Students have to put on display their art pieces and School Plays. This school festival arc was about Yuno's quest for a topic for the aforementioned art piece.
School Play - Yuno is the stage technician for one in the School Festival, and Miyako, realistically, the horse. In that same episode, Yuno walks in on Hiro and Sae practicing for a play, ending up in the above-mentioned Not What It Looks Like moment.
Schoolgirl Lesbians - Subverted when Yuno runs into two flustered girls in the bamboo bushes behind the school, who tell Yuno not to tell anyone as they run off; Yuno calls out to them asking if they're going out, which they quickly and strongly deny (most likely just visiting a statuette there). Miyako also at one point thinks that Yuno has a crush on a female sempai and encourages her to "follow her true feelings". And back in Sae's junior high days...
Chika: She even got valentine chocolate from other girls in class. Miyako/Yuno: I knew it! Sae: What do you mean you knew it? Miyako: Sae-san, is that where you got that wealth of love stories to tell? Sae: No way. Chika, don't tell such useless things. Hiro: It's nothing shameful to hide. Sae is also cool from the eyes of a girl. Miyako: Whoa! What a bold statement!!
Natsume is painfully tsundere for Sae (see below) but can't catch a break, being the losing corner of a Love Triangle. Played up to the hilt in episode 12 of x365 when Sae joins Natsume for lunch, with the latter first getting combative before quieting down. We even get a few Male Gaze shots in that episode; when Natsume watches Sae enter the cafeteria (focusing on her hips), watching her eat (focusing on her lips), and again as Sae walks away... The flowers, the spring out of her hair, and the luminescent blush seem to put it straight into Schoolgirl Lesbians territory. The very last episode has her praying at a shrine to become more honest with her feelings. And guess who wrote that passionate fan letter that Sae got?
She does get a few moments of happiness later on, including the x365 OVA where she gets to ride a bike with Sae to help return something one of the soon-to-be-tenants has dropped, after being ordered to 'get on' and to 'hold on tight'.
And this all began thanks to Sae just being nice to Natsume when the latter was scared and upset at being at a new school by giving a few kind words and a smile. The latter was having a very, very bad day up to that point.
Sex As Rite-Of-Passage - (cough) When Yuno says something that sounds mature to Yoshinoya, Yoshinoya worries that Yuno has "become mature" before her, complete with a rather suggestive imagination bubble of Yuno.
And in a similar vein in the first Hoshimittsu TV special, Yoshinoya is horrified when Miyako, sporting a noticeably bloated stomach, tells her she "beat her to it" ("it" in this case being a newly-opened family restaurant, where Big Eater Miyako rather over-indulged).
Shipper on Deck - In one episode of Hoshimittsu, two of Natsume's classmates downright encouraged her to get over her contrary responses to spend some time with Sae, getting her to walk Sae home (across the street).
Shiritori - in an episode the group played this while sitting around watching Miyako's apartment leak.
In the manga chapter where they go to Destiny Land, they use it to pass the time waiting in line.
x365's opening starts with a "bouncing girls" sequence very similar to the one in Azumanga Daioh.
In episode one, you can see that Yuno has six volumes◊ of Hidamari Sketch manga.
And then there are of course all those cosplay outfits as worn by Yoshinoya-sensei. Her statement that she is "forever 17" is also a reference to seiyuu Kikuko Inoue.
Miyu Matsuki (Yoshinoya's VA) is on the same radio show as Inoue, Rie Tanaka, and other members of the "Forever 17 club." So it could be a self-reference, rather than a reference to Inoue specifically.
In episode 6a of x365, starting at around 6:40, you can see a doll sitting on a pillow in Hiro's room. Over the next 2 minutes or so it changes into chibi versions of various characters, including Yoko and Nia from Tengen Toppa Gurren Lagann.
All of the show's soundtracks have cover art that references a The Beatles album. The first season's is "Abbey Road", x365 was "Help!" and Hoshimittsu is "A Hard Day's Night".
Many of the over head shots in the anime are done in Three-Quarters View. Some shots of the apartment layouts go even further with hidden rooms containing graphic tiles and icons straight out of Dragon Quest.
Smashing Watermelons - There is no Beach Episode (only a pool episode) in this series. However, Yuno finds an inflatable watermelon-like beachball in the shed and plays around with it in this manner, "just to get the feeling."
The Nintendo DS game has a watermelon smashing minigame, where you are blindfolded (the screen blanked out) and have to listen to the other girls' directions to successfully hit it.
Sprouting Ears - As a one-time thing, Sae sprouts cat ears and tail purely out of surprise/confusion when Yuno's dad angrily points at her and shouts "It's YOU!" as she walks in. (He mistook her as Yuno's boyfriend based on a stray hair he found in Yuno's room — after first asking whether it belonged to a cat.)
Squick - An In-Universe use: Hiro has this reaction when she's rummaging under the sink for something to eat. She manages to grab a very old, very moldy orange.
Nori: It- it's not like I keep it because I think it's cute or anything!
Tanabata - The episode of x365 described in Crowning Moment of Heartwarming takes place on Tanabata; after Sae and Hiro make up, the girls spend the afternoon and evening decorating a bamboo the landlady planted in the garden, and hanging their wishes on it.
Tomboy and Girly Girl - two pairs. Miyako as the extroverted and boyish type and Yuno being much more introverted and soft-spoken one; Sae's "masculinity" was often lampshaded by Miyako while Hiro is overtly declared by the author as "wife material."
Let's see if Nori and Nazuna became the third...
Too Long; Didn't Dub - One particular example are the two strips on page 90 of Yen Press' Volume 3, quoted verbatim below:
Strip 1, from frame 3 on:
Miyako: Maybe it's "chijou no motsure." (Lover's fights)
Two-Teacher School - Sort of averted. There are only two named teachers, Yoshinoya and Mashiko, but there are a lot of unnamed teachers teaching other subjects — Yoshinoya and Mashiko appreantly only teach studio arts.
Wasn't That Fun? - In one episode, the girls visit a water park and go down a very high waterslide. Yuno screams the loudest of the four girls, and seems genuinely terrified as she goes down, but when she comes up out of the water, she's all smiles. "It wasn't as scary as I thought!"
You Gotta Have Blue Hair - Sae and Chika are actually blue. Hiro was pink, but it changed into a peach-ish color in season 2. Miyako is blond and Yoshinoya's hair is green. Nori's hair is a blue/green mix and Matsuri's is a very pale lavender.