Abusive Parents: Sakuya's father, while not physically abusive, has incredibly racist views that he indoctrinated his son with and seems to care more about Sakuya's prospects as the future family heir than his own personal wishes, something confirmed in Sakuya's extended ending where he's kicked out of the house after he confesses to his father that he wants to become a musician. Not only that, but the Bad Boys Love route reveals that said father refused to feed his stepson Yuuya unless he abandoned his full brother's egg and it was only through Yuuya's tricks that said brother even had a family to begin with...and that brother was none other than Sakuya. In other words, Sakuya's "father" would have had him thrown away were it not for Yuuya actually caring about him and, as Yuuya points out, he would disown his "son" in a heartbeat if he ever found out about this.
Author Appeal: Oko San is based on moa810's own pet bird.
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.
Blood Knight: Sometimes the heroine expresses her barbaric heritage, for example, "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."
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.
Bunny-Ears Lawyer: Kazuaki is a world-famous math genius... and a narcoleptic who falls asleep in the middle of talking.
The player character may also be one, since she's apparently already passed a year at one of the most demanding private high schools in the world, despite being a cave-dwelling barbarian, and sometimes protests things in rather erudite terminology for someone who couldn't finish her reading assignment.
But Thou Must: 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, your three choices all say "Yes."
It Gets Worse. He doesn't carry your head around at the moment of dialogue. He has attached it to Labor 9, or the Scarecrow. You can only answer "yes" because you don't have free will anymore.
Chivalrous Pervert: Yuuya, who amongst other things tells you that doves reach sexual maturity after only one year and interprets the act of looking at nest-building materials in a specific way.
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.
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?
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.
Dumb Muscle: You start with 1 wisdom, 800 vitality, and 5 charisma, and you do not get more than about 35 to 40 possible points of stat increase throughout the game.
Genre Shift: If you take the Bad Boys Love route, the game shifts from a humorous pigeon dating sim to a dark mystery/thriller. Anghel's route also unexpectedly turns into a battle RPG close to the end.
Fridge Brilliance: It does finally explain why, compared to your Wisdom and Charisma, your Vitality score is so humongous: in this battle it doubles as your Hit Points!
GIS Syndrome: Subverted. Stock photos are used for the bird characters and the loading screens, but they are properly cited in the credits.
Government Conspiracy: The Hawk Party's Operation Hurtful, which includes the creation of the H5N1 virus. On the other hand, they also get angry if you don't hook up with anyone.
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.
Idle Rich: If you join the student council, you can bully Sakuya into helping clean the office at the end of the semester, which ends with you having to teach him how because he's never done his own housework before.
I'm a Humanitarian: The birds have no problem with eating poultry. And, if you focus on Doctor Shuu, then he cooks Yuuya into something resembling a roast chicken.
When you die in 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...
Poster on the Let's Play thread: You are now realizing that without Anghel and Okosan, the joke characters, all the main characters and all human life would be gone by now.
Let's Play: Angie Gallant's legendary let's play of the free demo version might just be the reason you're here right now. She has now done a follow up for the full game.
Mad Scientist: Doctor Shuu wants to feed steroids into Oko San just to see how his body will react to them. It turns out that he is a researcher for the Hawk Party.
Mayfly December Romance: Yep, this game acknowledges the difference between human and bird lifespans.
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.
Medium Awareness: "What's the number in the top-left-hand corner say?"
Meido: Ryouta dresses up as this, and you can join him.
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.
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?!?"
Notice This: On the Bad Boys Love route, several plot-important phrases are highlighted yellow.
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.
Overly Narrow Superlative: The English download site for the game describes it as "the world's greatest pigeon dating sim".
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...
Phenotype Stereotype: The ordinary guy is a rock dove, fan-tails tend to be full of themselves, the mourning dove is introverted, etc. Fan-artists also do a bit of this by portraying Hiyoko as short-haired, often blonde.
Precision F-Strike: If you tell Doctor Shuu that Yuuya is lying, Shuu thanks you before kicking you out of the infirmary, saying that he needs to discuss this with Yuuya ... alone. Yuuya's reaction: "...Shit."
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".
Relationship Values: As usual for the genre, although they are not shown to the player.
Removed From The Picture: If Hiyoko is on Kazuaki's route, she finds a photo dropped by him that has the photographed bird almost completely marked out.
Which, in the Bad Boy's Love route, we learn was probably a photo of his dead brother, Nageki.
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.
Serious Business: For Oko San, it is pudding. In his ending, he quits school to quest for the true pudding, and you can join him.
The Bad End if you don't go all the way with any romance has a very specific grim reaper screen!! It also has double exclamation marks!! Like all over the place!! And one of the inventory items is a Nintendo 3DS amongst other things!!
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.
Switched at Birth: Yuuya swapped his stepfather's egg with his dead father's egg containing Sakuya so that his brother could have a family and a home instead of being thrown away on his stepfather's orders.
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 Nanaki as bemaided birds as well.
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.
When Sakuya asks the player what she loves, she answers "udon." Though she also can't sit still in class unless she's had some red meat, as she tells Ryouta in the first cutscene.
Twenty Minutes into the Future: In the Bad Boy's Love route, you find out that the game actually takes place in the year 2187!
Wholesome Crossdresser: You will always see Ryouta in a maid's uniform for the Maid Cafe, and if you follow him down his arc you'll find he also works at a transvestite cafe... and goes by the name "Coolene". Of course, he's working there so he can support his mother, but you can ask him to leave.
Widget Series: The premise of the game is considered to be very far outside the mainstream box.