Bad End: As usual for the genre if you don't go all the way with any romance.
There is also one caused in the demo version by staying in the infirmary to wait for Ryouta. Doctor Shuu cuts your head off and stuffs it in a box. The normal ending for Doctor Shuu might also be considered this.
Big Damn Heroes: On the Bad Boys Love route, just when things look at their bleakest with a trapped Kazuaki and Anghel dying from poison gas and a broken Ryouta submitting to Doctor Shuu, Oko San and Sakuya show up to help.
Bread, Eggs, Milk, Squick: The various clubs at the school include the track team, the student council, and the birdwatching club... which, in a school for birds, basically amounts to voyeurism of (and by) school students.
Break the Cutie: Happens a lot in the Bad BoysLove route. Ryouta, however, by far gets the worst of it, particularly when the identity of Hiyoko's killer is revealed.
Breaking the Fourth Wall: Hiyoko is aware of the ending credits sequence that happens after getting Azami and Blaster together and interrupts it angrily. In Holiday Star's fourth episode she recaps the third one out loud for "the camera", and when Nageki asks about it she says people might have forgotten. He says being so aware of the camera doesn't seem very professional.
"Whatever! It's better to give the readers a hand!"
If you join the student council then you are forced into the vice presidency. Fair enough: you're the only other person on it.
A creepy example occurs during Doctor Shuu's best ending in the full version: when he asks you if you love him after he's killed you and is currently carrying your severed head around and interprets her head bobbing up and down in the jar as an answer, since your three choices all say "Yes."
Cerebus Syndrome: Most of the game is rather silly and lighthearted. Then you get on the Bad Boys Love route in the full version, or play the last chapter of Holiday Star...
Club Stub: The Student Council. If the heroine joins, there are two members. Otherwise, it's just Sakuya, who doesn't seem to be in touch with his class's opinions or even want to be there.
Coca-Pepsi, Inc.: A religious example. Hiyoko mentions that she comes from "Shint Buddhist" family. Both Tanabata and Christmas are celebrated in this universe. Anghel mentions reincarnation in his ramblings, but his human portrait also has crosses (a symbol of Christianity, a religion, which has nothing to do with reincarnation) and his name means "Angel" -angels belong to Abrahamic religions, not to Dharmic ones.
Cowboy Bebop at His Computer: One of the game reviews mentioned the protagonist's name - Cloaca Mahoney - as a downside. In fact, "Cloaca Mohoney" is only a name Angie Gallant chose for her famous walkthrough of the game. See, kids? That's what happens when you don't play the game before reviewing it.
Creepy Physical: The doctor, Iwamine Shuu, offers to give you some interesting drugs. He also promises to examine your insides most intimately once he's done preserving your head.
Cry for the Devil: Doctor Shuu appears to rocket-jump over the Moral Event Horizon in the Bad Boys Love route. Then he reveals that he's doing all of this because of his unrequited love for Ryouta's father and sincere desire to fulfill his dying wish. It doesn't excuse the horrific things he's done up to that point, but it does make one feel at least a twinge of pity for him.
Damning With Faint Praise: In the first scene with Ryouta, he offers to make breakfast for our heroine. Her answer? "Maybe I'll take you up on that, if starvation looms!" Ryouta's cooking is maybe preferable to starvation? Gee, thanks for that vote of confidence... Which is odd, because she says that Ryouta's cooking is delicious if she talks to him during the class hike. Maybe it was just her typical Large Ham way of speaking?
Ryouta is a vegetarian, and the protagonist can't sit still in class without meat.
The protagonist is a hunter-gatherer, so one can assume this line describes her pride in her independent lifestyle as opposed to being catered to.
"That's terrible! I mean, Okosan is a nutcase and I don't know what he's saying half the time, but he really does like pudding!"
Dub-Induced Plot Hole: In the English translation of the demo, Kazuaki refers to the bird in his marked-out photo with female pronouns, implying that she was his dead lover. This became a bit awkward when the full game version came out and revealed that Kazuaki's photo was most likely of his dead brother Nageki. Fortunately, this was corrected in the separate English translation for the full game.
If you take the Bad Boys Love route, the game shifts from a humorous pigeon dating sim to a dark mystery/thriller.
Holiday Star's first two stories are loony absurd adventures, with minor darker hints here and there. The third story is similar, a fantasy-RPG-ish romp. Until the end of that one, and the fourth is nightmarish and aferlife-y.
100% Completion: Getting at least one ending for each bird unlocks the Bad Boys Love route, and completing that in turn gives you a "thank you" picture after the credits a full set of documents in the Library. Getting all of the endings for each bird unlocks a post-BBL epilogue, the last Gallery image, and a Library item with a bonus scene.
In the main game, only the protagonist and Anghel can see Nageki, though Anghel only shows this once as an optional scene on his route. During the BBL route, it is revealed that Ryouta can as well. Also referenced in the Drama CD when he talks to his "dead friend" Nageki in the library about one of the seven mysteries of the school: students who draw in library books are said to get cursed. As Ryouta suspects, there is actually some truth to this...
In the manga, Okosan can also see him, and in Holiday Star it's said that only the pure of heart can see ghosts.
Killed Off for Real: Hiyoko and Yuuya on the Bad Boys Love route. Although if you get the full ending, you find that Yuuya was saved just in time, and Hiyoko might be revived.
Killer Rabbit: You will never, ever look at Chukar partridges the same way again. Or King Quails, especially the darker colored ones.
A group of fans known as Team Hatoful has done a series of voiced playthroughs of different routes of the first game - specifically Anghel's, Bad Boys Love, Ryouta's and Sakuya's routes - and has also completed a blind run of HolidayStar. Notable for, among other things, taking Yuuya's Handsome Lech tendencies even further, giving the French Sakuya a fake British accent, making Shuu sound like Severus Snape, and turning Tohri into a German-accented Large Ham.
Lighter and Softer: The drama CDs and - for the most part - the manga are pretty much played purely for comedy and don't have the same tendency for twists and pathos as either of the games.
Meaningful Background Event: Blink and you'll miss it, but your first clue that things in this game aren't quite as cheerful as they first seem comes when Hiyoko decides to go for a run: One of the things she passes is the post-apocalyptic remains of a city.
Meido: Ryouta dresses up as this, and Hiyoko can join him.
In the bonus content you unlock by completing Bad Boy's Love, Sakuya and Kazuaki are dragged into it as well.
The Merch: There are already plans for tote bags, pins, St. PigeoNation ID cards and more. Various styles of St. Pigeonation bags, shirts, cups and even a thong with Yuuya on it can be found at the Cafepress store
Missing Mom: If you focus on Ryouta, then you find out his mother dies.
Mood Whiplash: The endings of Ryouta and Nageki's routes can come as quite a shock if you've grown used to the game's silly and comedic tone. The Bad Boys Love route in the full version, even more so. The manga, which is largely cheerful absurd short comics, also has several chapters end with Kazuaki explaining the history of the setting - like how a plague swept humankind and killed seventy percent of them.
"Not Making This Up" Disclaimer: The official website has many of these. People trying to get others to play this game typically have to use lots of these too, as most rational people's initial reaction to hearing about it is something along the lines of "Wait, something like this actually exists?!?"
Official Couple: It's not definite, but Ryouta seems to be the most canon love interest for Hiyoko as he's the one who stays with her spirit in the hopes of him being able to be cured of his disease and her being able to be transplanted into a body someday in the good ending to the Bad Boys Love route, the last route you can unlock.
Holiday Star suggests that it's Nageki, or at least has Ryouta fear this, but the Holiday Star route is distinct and doesn't overlap.
Ominous Save Prompt: This happens at the end of every chapter in BBL. This is also the only time players can save during BBL as well.
Bird of Mass Destruction: The Bad Boys Love route reveals that Nageki harbored a disease that caused all humans who got too close to him to drop dead on the spot, which was the main reason he killed himself. Unfortunately, some of his body parts were saved by Doctor Shuu, who intends to make Ryouta the new carrier...
The Promise: The Bad Boys Love route is jumpstarted by one.
Pun-Based Title: The title is a mix of hato, the Japanese word for pigeon/dove, and "heartful". The paid version of the game is subtitled "-Hurtful Complete Edition-" as well. Then there's Hurtful Boyfriend and Operation Hurtful.
Punch Clock Villain: If you don't finish any romantic storylines, a meeting of the Hawk Party condemns humanity and orders them exterminated... then adjourns for coffee.
Punny Name: The (quail) teacher and (partridge) doctor have surnames punning on the Japanese for "quail" and "partridge". The library freshman's personal name is based on "nagekibato", the Japanese word for "mourning dove". Both the partridge and the quail are operating under assumed names, so this was probably deliberate on their parts.
Rainbow Speak: On the Bad Boys Love route, several plot-important phrases are highlighted in yellow. Really important things are highlighted in red.
Played for Laughs as they are not very important: "Hiyoko levelled up! Wisdom increased by 5!"
They become a bit more important in the full version where you need to boost the appropriate stats to get the best endings for Doctor Shuu, Sakuya, and Oko San. Additionally, Anghel's route features a turn-based RPG battle and while it's mainly used for parody, it is possible to lose it and get a bad ending if you botch it.
Save Game Limits: The Bad Boys Love route, in contrast with the main Otome route where you could save any time you wanted, lets you save only at certain points in the story.
Seven Deadly Sins: All of the main birds fit into this if you include the eighth deadly sin that is mentioned on the trope's page.
Wrath: Kazuaki. He murdered the original Kazuaki, stole his identity, and nearly murdered Shuu to get Nageki back. The original Kazuaki fits into this too, refusing to let people leave the Holiday Star all because of one person.
Sloth: Sakuya. He sits around and does nothing because he believes it's beneath him. Alternately Pride, by which he can be manipulated and which blinds him to a lot of things.
Envy: Ryouta. The scene with him worrying over Nageki and Hiyoko in Holiday Star. Case closed.
Gluttony: Okosan. His pudding obsession, and his Big Eater habits.
Pride: Anghel. He believes he is a pure servant of God, and his world is based on how HE thinks things should be.
Greed: Shuu. He only cares for his own knowledge. He was even willing to keep everyone trapped on the Holiday Star to continue his research.
Despair: Nageki is a mourning dove, whose name means "lamentation" and is a very depressed freshman. The fact he is a ghost that committed suicide after completely losing hope as a result of the tragedies he was forced to suffer further supports this.
Probably his best, however, is unleashed upon Sakuya on Oko's route if you side with him during an argument between the two: "GIGA...DRILL...BEEEEEEEEEAK!!" Sakuya doesn't have a prayer after that one.
Star-Crossed Lovers: Anghel claims that Hiyoko and himself were this in a past life. A more straight example would be Hiyoko and Nageki on Nageki's route when he fades away after realizing that he loves Hiyoko.
When the heroine shows up on the wrong day for class, if you choose to return home, she tells Kazuaki: "I must return to my people with the spoils of war, lay my bloodied sword at the feet of my great king, and celebrate my conquest of all the lands from here to distant Macedonia."
Except for the student festival in fall, when your class does a Maid Cafe and Ryota briefly appears with a maid outfit drawn over his photo. This leads to the usual fanart of everybirdie crossdressing as maids, even those in other classes and the staff. Oko also appears in a maid outfit during his route, and the Library menu's post-BBL bonus scene shows Sakuya and Kazuaki as bemaided birds as well.
And Oko San's ICPSS portrait, while all other characters are rendered as Bishounen, is a bird in a school uniform.
In the full version, you can see the other classmates dressed up as maids for the Maid Cafe, and Ryouta fills in as a Miko at the local shrine for New Year's.
During the Radio session for Holiday Star, Ryouta explains that clothing isn't mandatory for birds, who wear clothes for protection against cold, fashion, or ceremonial purposes only.
There Are No Therapists: The bird society is developed enough to include everything from educational institutions to healthcare providers. However, mental healthcare isn't mentioned a single time in this series, so all the bird characters with personal issues are just left to get even crazier.
Two-Teacher School: The main game has only Kazuaki and Shuu. BBL shows us the principal, but only briefly and not while he is still among the living.
Uplifted Animal: It turns out that intelligent birds did not naturally come about...
Wham Line: "I wonder why he lied about going straight home...?"
Widget Series: The premise of the game is considered to be very far outside the mainstream box.
You All Look Familiar: The manga lampshades the difficulties of having three white fantails in the cast, and distinguishes them by giving Sakuya and Yuuya accessories in bird form, while Oko San remains "nude". Less present in the actual game where their bird-photo images all have different poses, and of course their human-style portraits are all different.
Tropes specific to Holiday Star include:
All Just a Dream: During Holiday Star, Hiyoko can discover Tohri's nefarious plot. Cut to her in a cafe with Ryouta and Kazuaki, saying "Crazy dream, huh?". Ryouta falls for this trope and gets told that she was joking. During the shrine visits, Yuuya halfway confesses to Hiyoko that he's not just an Ordinary High-School Student, but chickens out and says he was talking about a dream.
Always Night: The oneiric Holiday Star is this, since it's in outer space. And also because Holiday Star is an Eldritch-hive mind composed of troubled wandering souls who cannot leave.
Citizens: "Everyone knows midnight comes after predawn. And after that, dusk, then midnight again, then predawn, then midnight. Time swings back and forth like a pendulum, after all."
Battle Butler: Sakuya's butler Albert Alain Alkan. Also a typical Scary Black Bird. He is actually an infamous assassin who was contracted to kill Sakuya, but later hired by him for protection.
Blood Science: Mad Scientist Tohri Nishikikouji uses Anghel Higure's blood to help power his canon and materialize the will and drive of fanboys and fangirls, turning it into an offensive beam capable of destroying buildings.
Don't Fear The Reaper: The Conductor in Holiday Star is pretty laid back and gives advice like "I dunno, kiddo. We never recommend haunting as a deathstyle choice, y’know? Too easy to go all black and bitter." It's revealed at some point that he is Death, as seen in the Bad Ends, and Hiyoko considers him her friend. They go all the way back to the demo version!
Empathic Environment: Holiday Star's Mount Pudi has rain on it when the emotionally troubled Nemo/ imposter Kazuaki cannot remember his real name.
The Throne Room on Holiday Star also Turns Red when The King turns One-Winged Angel in desperation to keep our heroes on Holiday Star.
Epiphanic Prison: Holiday Star is a place that traps souls who are emotionally troubled and/or weak willed. The only way to leave this place is if enough of the trapped individuals realize they have something worth living for in life/reality/outside Holiday Star.
Keystone Army: The enormous hydra-like "Increased" King can only be defeated by Nageki using his planisphere to burn down The King's lighthouse.
Lotus-Eater Machine: The King's lighthouse projects Holiday Star's inhabitants' greatest desires to keep them perpetually happy.
Lunacy: In the third chapter of Holiday Star anyone watching the lunar eclipse will immediately enter a dream-filled coma/proceed onto the oneiric afterlife.
Maybe Magic, Maybe Mundane: In the last two chapters of Holiday Star everyone who watches the lunar eclipse immediately falls unconscious. While unconscious they dream they are riding a galactic railroad, which ultimately leads to the afterlife. In the real world J.B. Leone explains that everyone who watched the lunar eclipse is in a coma due to avian brains being unstable from unnatural development. So is the visit to Holiday Star the protagonists actually visiting an ethereal plane, or is Holiday Star completely imaginary and due to neurons misfiring in their unstable brains?
Nonstandard Game Over: In Holiday Star this happens if the player chooses a wrong choice during the fourth chapter. This wrong choice causes a character to get absorbed into The King's twisted hive mind, which The King considers living "happily ever after."
Can also happen if the player fails to transform into a magical girl by flubbing the transformation line in the second chapter.
Power Crystal: In Holiday Star there are three of them: the garnet, the lapis lazuli, and the topaz. However, only the topaz is the stone which will get everyone the good ending; the garnet and lapis lazuli are fakes.
Scenery Porn: The entirety of the water color-rendered Holiday Star is this.
Tastes Like Friendship: Once The King is defeated and his Holiday Star is destroyed, he is left totally distraught and alone. However, once he joins The Migrant and the former Holiday Star citizens on the galactic railroad, they offer him sweets such as caramels and sugar cubes to cheer him up. Other stories in Holiday Star do mention The King/original Kazuaki as a sweets-lover, so perhaps The Migrant and the ex-citizens offering him his favorite foods would mean the start of a new friendship as well as emotional healing.
Tempting Fate: In Holiday Star, Sakuya proudly boasts that there's no way the thieves will be able to get into the council room. Hiyoko refers to this as "raising a flag", and when the inevitable happens she and Ryouta call it "flag retrieval" - they're terms commonly used to refer to visual novel gameplay.
Uncanny Village: Holiday Star is a gorgeous place and its citizens and ruler are friendly enough. But why does The King briefly become monstrous looking whenever he gets upset?
Viral Transformation: Anyone who stays on the Holiday Star for too long will lose their individual identity and become a King/part of The King himself.