Some mention should go to Tsukushi's parents. While they're generally flighty but loving, one chapter has her coming home from school to find them and her brother packing their things: they were moving out to the city, not taking Tsukushi, or planning to tell her until that very day. Keep in mind Tsukushi is in school and has no job... Her parents promise to send money for her, but when she finally gets a letter from them, it says that they don't have money to send her yet, so here, have some strips of seaweed. Tsukushi honestly thought she'd starve, and probably would have if not for her friends. They are also incredibly stupid, want Tsukushi to be a gold digger and keep losing money on pointless things like pachinko resulting in their poverty...
Accidental Kiss: Happens in the live action version between Tsukushi and Tsukasa due to an unlikely trip-fall-catch.
In both the Manga and Anime, this was how Tsukushi lost her Sacred First Kiss to Domyouji.
Adaptation Distillation: The jDrama neatly compresses the sprawling plot of the manga into a much smoother, shorter story.
Adrenaline Makeover: Tsukushi goes through one when she decides to stand up to the F4. Most obviously shown by her taking down her pigtails.
Airplane of Love: Twice, and both more literal than most cases. First when Tsukushi watches the plane in which Rui is flying to Paris take off, then when she watches Tsukasa's jet take off for New York.
All Girls Want Bad Boys: Tsukasa is definitely the most rough-edged and morally questionable member of F4, and the one who gets the girl (although Tsukushi was initially turned off by his Jerkass ways and preferred the more subdued Rui.) Also a possible factor in Yuki's feelings for Sōjirō.
And it actually comes up later in a humorous fashion Tsukasa and Tsukushi are close to making love, but Tsukushi is so nervous that she starts crying. It remains an awkward moment for them until Tsubaki walks in on them, sees Tsukushi crying and thinks Tsukasa is trying to rape her. Even Tsukushi trying to reassure her doesn't stop Tsubaki from once again kicking Tsukasa's ass.
The Big Damn Kiss: In the J-Drama, Tsukasa and Tsukushi have one of in both season finales. The first one is particularly epic.
Big Damn Movie: Hana Yori Dango: Final, the film conclusion to the J-Drama series, changes the plot from a melodramatic Will They or Won't They? to a globe-spanning quest for a missing tiara. Subverted when the whole thing is revealed to be a plot by their friends and family to test the strength of their relationship.
Big Fancy House: Several. We see Shigeru's, Sakurako's, Shizuka's, Akira's, Sōjirō's, Rui's and three of Domyoji's, but particular focus is given to the Domyoji primary Tokyo residence, which is enormous. Every wealthy character is actually implied to have several moreBig Fancy Houses around the world.
Category Traitor: A big tool in the F4's corruption of the student body; if you don't at least seem to actively participate in the public shaming and bullying they assign to those who they "red card," then you're likely to be the next recipient.
Dances and Balls: The party during Tsukushi's vacation with fellow students on the cruise.
Disappeared Dad: While Tsukasa's father is referenced occasionally in the manga, he is never seen and it's stated that Tsukasa himself hasn't seen him in years. In the drama, he is simply not mentioned at all until the movie.
Researching the Makino's financial situation, Kaede visits their home and offers them a suitcase containing ¥50,000,000 in cash in exchange for Tsukushi to never see Domyouji again. Tsukushi's mother - who has been the most vocal with her lamentations regarding their lack of money - goes to the kitchen, gets a bin of salt, and cooly proceeds to pour the contents over Kaede's head saying "Take your money ... and get out," making this her Crowning Moment of Awesome.
Heel Face Turn: Tsukasa, Sakurako, Thomas, Junpei, both of Tsukasa's parents, the list goes on. Probably the only "villains" who don't are the Terrible Trio; however, don't expect any of these to be perfect nice guys and gals after the switch.
Heel Realization: His relationship with Tsukushi forces Tsukasa to go through this. This becomes a Crowning Moment of Funny in at least one continuity where, after having allowed himself to be brutally assaulted to protect Tsukushi, he writes her a letter thanking her for teaching him what it's like to get beat up.
Heroic BSOD: Rui, as a product of his upbringing, tended to have panic attacks. Shizuka helped him get rid of them.
Tsukasa goes through this when he sees photos of Tsukushi in bed with another man. He's so out of it that he doesn't even notice Sakurako taking him to her house, or Tsukushi screaming for help from classmates brutally hazing her.
Karma Houdini: The F4's bullying borders on Kick the Dog territory at times, up to and including Tsukasa authorizing some underlings to gang-rape Tsukushi (though varying media have different levels of how explicit the authorization was). They never particularly suffer any consequences.
Laser-Guided Karma; Tsukasa does get beaten nearly to death on one occasion and is stabbed almost mortally on another, add to that all the emotional tolls he goes through throughout the series. It does occasionally suck to be Tsukasa.
Malaproper: Tsukasa. "Anyway, the point is, you sleep-talk during RAM sleep!"
Mafia Princess: Akira's a bit of a male version in the jDrama, and his little sisters qualify.
Manic Pixie Dream Girl: Shigeru tries to become one of these for Tsukasa. When he makes clear that he doesn't like her that way, she resorts to play Shipper on Deck and get him and Tsukushi together instead.
Meaningful Name: "Tsukushi" really is a stubborn weed (a type of horsetail, to be exact), and the character holds herself to it.
Mood Whiplash: the serious tone of the story gets interrupted with commercial breaks marked by humorous sitcom style antics of the guys trying to peek at Tsukushi in a bubble bath, especially jarring when it is seen in the middle of an attempted gang rape.
Pair the Spares: Sakurako and Kazuya might be in their way to this, in the end of the anime.
Yuki and Soujirou are teased as a potential secondary love duo in the Japanese live action version, though it never comes to fruition. Their Korean live action counterparts — Ga Eul and Yi Jung, respectively — do end up paired up in the end.
Parental Neglect: All members of the F4 (except perhaps Akira) seem to display this to some extent, but Tsukasa seems to have been the most negatively affected by it. Ironically, when his mother starts paying attention to him, his entire life takes a turn for the worse.
Pretty in Mink: Male example; Tsukasa wears a fur-trimmed coat to the zoo.
Pun-Based Title: The title is an old Japanese Idiom: "Sweets before (are better than) flowers." (The practical beats the purely emotional). Except they use a different "Dango" character (a fairly obscure word for boys) instead of the character that means "sweets".
Shizuka was flat out flattered that Rui felt strongly enough about her that he would attempt to rape her. This turned into a Near Rape Experience when he stopped to puzzle out just how wrong it was that she was entirely accepting of this.
Second Love: Although Tsukushi initially loved Rui, she ends up with Domyoji.
Sheltered Aristocrat: The F4 and assorted minor characters. Notably, all of the common subtypes are represented in the F4 (Sōjirō and Akira are clownish but charming buffoons, Tsukasa is the pompous, arrogant meanie (who is also a buffoon), and Rui isthe composed, reserved and usually highly intelligent one).
Team Dad: Akira is this to an extent. He doesn't particularly care about forcing morality on the group (and probably couldn't if he wanted to) but is the general mediator for conflicts and seems to take it upon his shoulders when the group isn't getting along, eventually leading to him getting in a fistfight with Tsukasa when the latter won't stop stirring up drama with Rui.
The Teaser: Used in the J-drama. There might be a recap mixed in with it, too.
There Are No Therapists: Tsukasa has displayed serious behavioral problems his entire life, Rui was said to be pretty much mute and uncommunicative as a child. Neither of their sets of parents, despite being of considerable means ever sought professional help to address this.
This Is Reality: (Paraphrased:) "Falling on top of your worst enemy and kissing her? This isn't a manga, you know!"
Through His Stomach - Attempted by Umi on Tsukasa when he was suffering from Amnesia and had forgotten all about Tsukushi. In a potential Crowning Moment of Awesome for Tsukasa, he rejected the romantic upstart because her cooking wasn't like Tsukushi's.
Traumatic Haircut: Tsukushi gets her hair ruined by a bunch of bullies and has to get it cut, first by her mom and then by Rui.