Unlucky Busty Girl

In a series where the main character has several girls he could end up with, he often chooses the one that does not follow Buxom is Better, for whatever reason. It may be that the author is trying to send a message about beauty being worth more than looks, or maybe the author simply doesn't like large breasts. Whatever the cause, the poor busty girl gets left in the dust by her more flat-chested rival. In most cases, the bustier girl is just as interesting and developed as any of the other characters. Related, of course, to Unlucky Childhood Friend. Contrast Buxom is Better.

Anime and Manga
To say nothing of Shirley, at least the other two. "Soul: It's not the size or the shape that matters."
 * Most of Rie Kugimiya's pettanko tsunderes tend to prevail over their bustier rivals due to First Girl Wins:
 * Tora Dora: main character Ryuji ends up with Taiga, who is notably flatchested. Ami, on the other hand, isn't quite so fortunate.
 * Zero No Tsukaima: though still largely in the throes of Will They or Won't They??, Saito has expressed primary romantic interest in Louise over the more buxom Siesta.
 * As well as Tiffania, Henrietta, and Kirche, just to name the more pronounced ones.
 * Shakugan No Shana: Yuji chooses Shana over Yoshida.
 * While Hayate the Combat Butler's Nagi completes the "Four Tsundere Wonders", she does not seem to have a busty rival. Maria is her surrogate Cool Big Sis, so she doesn't count, and Ayumu (aka "Hamster Girl") has very average sized breasts and is most likely the Unlucky Childhood Friend.
 * Athena is Nagi's rival, since Nagi and Athena were originally the same character. It's also been said a few times in a non-romantic setting. Athena's combination of childhood friend and busty girl makes her a very likely candidate for this trope.
 * She still doesn't know about Hinagiku, who's flat-chestedness is made fun of more than Nagi's (partially due to being a couple years older), loving Hayate though she certainly suspects it. Hinagiku however, knows about Athena and Hayate's past relationship and feelings for one another and how Athena is quite busty. Only time will tell if Rie Kugimiya's streak will hold up with a non-Lolicon flat-chested girl and another busty rival.
 * Hidan no Aria: Aria's the main girl, while Shirayuki takes this trope, and actually combines it with the Unlucky Childhood Friend trope.
 * In Devil Hunter Yohko, protagonist Yohko Mano notes that despite being more buxom than most of the other characters, she has terrible luck with her love life -- a fact that has ironically allowed her to be The Chosen One, since her superpowers are a Virgin Power.
 * After she gets her powers, the terrible luck with her love life stems from all the time she has to spend hunting devils instead of hooking up with guys.
 * In Midori no Hibi, Seiji ends up going out with Midori, who is much less endowed than Ayase or Lucy.
 * Similarly, in Ai Kora (from the same author), Maeda goes with Sakurako rather than big-breasted Yukari (who's in love with him from the beginning even). What makes this trope apply even more is that he only paid attention to her in the first place was because of her boobs. She is more or less the poster child of this trope, the poor thing.
 * Tina and Taeko in Ai Yori Aoshi lose to Aoi, who is by no means Pettanko, but rather less busty than them.
 * Depending on your point of view, Kallen Kozuki and Milly Ashford have shades of this. Milly seems to realize it long before the end of the series, actively encouraging Shirley to pursue Lelouch. Kallen seems to come to terms with her feelings.
 * CLANNAD (at least the anime version) has Nagisa triumph over Tomoya's other potential love interests: Kyou, Ryou, Tomoyo, and Kotomi, who are all "larger" than her.
 * Doubled worse for Kotomi, because not only does the anime subvert Buxom is Better for her but also First Girl Wins as well.
 * Gantz has Reika, an extremely popular model, who falls for main character Kei Kurono too late; when she actually meets him, he's already going out with Tae, who is small by most standards.
 * Toshiue no Hito's Morino is doubly unlucky. She'd always hated the attention her boobs garnered till she used them to catch a truly Nice Guy. They had already broken up (mostly due to his impotence at the er, critical moment), when along came the board-flat lolita-like Ageha; now Tsutomu has no trouble getting it up. Way to aggravate the body issues.
 * Although it's not romantic, Soul rejects the busty Blair's offer to be her weapon and stays with Maka, whom he frequently mocks for her lack of breasts.


 * In Love Hina, Keitaro ends up with Narusegawa, instead of the more endowed Mutsumi. Although Narusegawa isn't precisely a Pettanko, either.
 * Ano Hi Mita Hana no Namae o Bokutachi wa Mada Shiranai has Anaru, who pines away over Jintan, while the latter is obsessed with their confesses her own feelings to him.
 * Ranma ½: Shampoo and Kodachi both have significant breasts, but Ranma ultimately prefers Akane.
 * It's pretty obvious Tsukune Aono of Rosario+Vampire is going to end up with Moka rather than Kurumu.
 * In Hekikai No Aion, Tatsuya preferred Seine over his more busty Unlucky Childhood Friend and the very developed mermaid.

Fan Fiction

 * In My Immortal, Ebony thinks she's this, but it's really Angst Dissonance.
 * Although she flips between this and being jealous of her friend for having bigger "bobs" than her.

Film

 * In the Adam Sandler comedy Big Daddy, there are three main young female characters. The two more tomboyish ones end up happily married to successful white-collar husbands, while the busty one gets stuck in a dead-end job alongside her blue-collar (and laughably elderly) boyfriend at a Hooter's restaurant.
 * Talladega Nights: The Ballad of Ricky Bobby has the protagonist married to a stereotypical blonde, busty Southern bimbo named Carly. Later in the film Carly leaves Ricky for his former friend Cal, so Ricky begins a new relationship with his Pettanko (and Meganekko) assistant. The trope is subverted, however, when at the end of the movie the assistant undoes her blouse in Carly's presence -- and Carly grudgingly admits: "You got game."

Video Games, Visual Novels

 * Most BioWare games avert this, simply by using the same base torso model for all female characters, resulting in all possible Love Interests having equivalently-sized breasts.
 * Not so in Dragon Age II, in which Isabela is intentionally the bustiest female model. She will bow out gracefully if the player romances Merrill, whose character model is the same as most of the thin, lithe elves.
 * In Mass Effect 2, you can opt for Tali or Jack, two female love interests a little more under the bell curve in breast size, instead of the buxom Miranda.
 * Many games that allow you to choose your lover, like H-Games and Dating Sims can have this option.
 * Disturbingly done in some of the Bad Ends of School Days where Makoto ends up with Sekai instead of Kotonoha. Murder/suicide ensues.
 * Not really. Sekai isn't as stacked as Kotonoha, but she is quite big-chested. Now, if we're talking about Setsuna...
 * While the game itself gives you a choice, in other official works Lloyd of Tales of Symphonia ends up with his childhood friend Colette rather than the busty ninja Sheena.
 * Subverted in Final Fantasy VII: the first disc seemingly sets up Cloud with Aerith (though it's somewhat dependent on the player's actions), but then she dies, and Cloud ends up with Tifa.