Supporting Harem

Maybe that girl in the bottom right corner will win his heart? Yeah, she might have a chance.

A subtrope of the Harem Anime genre, a Romantic Comedy with one male protagonist, one female Love Interest, and a bunch of female side characters who also happen to be in love with the protagonist.

In these stories, the bigger emphasis is usually on the "romantic" part of Romantic Comedy, with the relationship building between the main Official Couple, and the side characters are only there for the viewer to like them, and maybe as a Romantic False Lead, to keep some drama between the main characters.

Certain character types like the Hot Teacher or the Ojou are likely to be members of this, as a straight romantic story with them at the center probably wouldn't work at all, or at least it would invite too many unusual plot points.

One of the causes for this set-up might be if it is the adaptation of a Visual Novel, where every girl got the focus of attention in her own route, but only one route got an adaptation.

Contrast with Balanced Harem, where several girls have equal prominence during the story.

Examples of Supporting Harem include:

Anime and Manga

Pictured above, The Familiar of Zero‍'‍s "Louise The Zero" is not just the title character, but also connected to the protagonist with a magical contract sealed by a kiss.
- Not to mention he confessed his love to her on the second season, and they even got married at the end of F. It doesn't stop three more girls from joining in the third season.
Clannad made it very obvious in the first scenes who was the main love interest, and the harem concept was entirely dropped during the first season anyways.
Rosario + Vampire has Moka as the only girl Tsukune clearly loves. The other girls try but there's nothing they can do.
- Until someone suggests the Tenchi Solution, that is. Other than the Official Couple, everyone thinks it's a great idea.
In Ah! My Goddess, there's never any question that Keiichi and Belldandy are the canon OTP, but that doesn't stop Skuld, Urd, Peorth, and Mara from being Pretty Freeloaders.
Keitaro and Naru from Love Hina are a very good example of this. It was obvious by the end of the first manga volume that Naru was Keitaro's "Promise Girl" and not even the "complications" that came with Mutsumi and Kanako could put a dent in it.
Negima is a very complex case of this since there is only one pairing that is really presented as it might be serious that is Negi and Nodoka early on which slowly became a Triangle with Yue, others are not that serious at all (besides Ako which is a whole other can of worms. Recently struck down in a good way). The early Magical World arc gave a lot more focus to Chisame than to most of the other girls, though not in a romantic way.
- Ultimately, most of the harem is unresolved at the end of the manga
Urusei Yatsura became this, although it started out as more balanced between Lum and Shinobu, only later Lum become more popular and Shinobou got an alternative Love Interest.
Ai Yori Aoshi is clearly this, as the lead girl has already won within the first few episodes. It's just that she and the male lead feel the need to keep their relationship a secret for various reasons, so the rest of the harem doesn't know this.
Ai Kora is this, as it seems clear that Sakurako is in the lead, with Yukari trying to make this a Love Triangle but not quite. Tsubame, Kirino and everyone else is just there to have one of Hachibei's beloved parts.
Subverted by Akane-Iro ni Somaru Saka, of all things. The entire series makes Yuuhi the main haremette and it's clear she'll win... But at the end, the main choses his sister Minato instead. There were some hints of this, but it mostly came out of nowhere.
Similarly subverted in Ichigo100%; while Junpei does initially express feeling in Satsuki, Tsukasa, and Aya, it becomes clear that Aya is his primary love interest. In the end, he chooses Tsukasa instead. Fans weren't happy.
Gender-inverted in The Wallflower, where it's blatantly obvious that the only real love interest for Sunako is Kyohei, especially when all the other guys get love interests of their own and begin trying various ways of getting Sunako and Kyohei together.
To LOVE-Ru started out as this, with Lala and Haruna getting all the screen time, with Word of God claiming they were intended to be the main focus of the story. However, as time went on, more girls were introduced and screen time evened out and it became much less clear who Rito would choose (it was a bit Lala-centric at first); in other words, it evolved into a Balanced Harem.
Another gender-inversion is Marmalade Boy, where from very early it's clear Yuu will win, no matter how much Ginta and the others try. At least they get their own girlfriends. It's also a straight example from Yuu's point of view. It's that kind of show.
Mayo Chiki has Subaru as the clear lead girl. How clear? Even the other haremettes love her!
It's pretty clear from the start of Ranma ½ who is going to be Ranma's love interest. While Shampoo and Ukyo get screen time here and there, Akane is on screen almost as much as Ranma is. She also gets his attention far more than the other girls. At the end of the series, Ranma inwardly declares his love for Akane and there is a Maybe Ever After ending. Take that as you will, shippers.
DearS, especially in the anime, is primarily focused on Takeya and Ren's budding relationship, though he also has Miu and Neneko chasing his affections. The manga, however, is somewhat more balanced. Takeya eventually gets to "make babies" with the entire DearS race.
After teasing things a bit, El-Hazard: The Magnificent World went right into this as soon as Makoto met Ifurita.

Literature

Twilight: Bella has Eric, Tyler, Mike, and Jacob all in love with her, but her One True Love is Edward. Not even Jacob giving her a Forceful Kiss in a later book could seriously challenge this.
A Gender Flipped example from the Mahabharata: Draupadi is married to 5 men at once (the Pandavas brothers), and though she does care for all of them one way or another, Arjuna is her favorite. This is because Arjuna is the incarnation of the god Indra, and Draupadi is the reincarnation of his wife Indrani.

Western Animation

In Galaxy Rangers, the attractive Lancer had quite a few admirers - Annie O, Maya of Tarkon, crime boss Daisy O'Mega ("Renegade Rangers" all but stated they had a shag), his former friend Darkstar... but the biggest Ship Tease was between him and Niko.