So You Want To/Write a Harem Anime

Boy Meets Girl. And Girl. And Girl. And Girl. The Romantic Comedy meets Love Dodecahedron, this is what happens when a Ordinary High School Student who is unlucky in love finally manages to roll a natural 20 on his CHA check.

The result is that the protagonist, previously unlucky in love, suddenly has several girls all vying for his attention at the same time.

One of the most popular Anime and Manga storylines due to its pure unadulterated wish fulfillment—this is the major setup for Renai Games (often called Dating Sims in the US), which are frequently made into an Anime as a form of cash in. But that shouldn't stop you from doing one, remember Tropes Are Not Bad, and the story of conflicted lovers is as old as time itself.

Much of the advice on Write a Magical Girlfriend Series also deals with harems as well.

Necessary Tropes

 * Fan Service: A Harem series is essentially a fanservice series. You need to make your characters very appealing both to the protagonist and to the audience. This includes specific ShoutOuts to the audience. Hadaka Apron, Beach Episode, etc etc.
 * Love Dodecahedron: You don't have a series without at least some relationship conflict. In most cases, this is at least 3 characters being in love with the hero, who is unable to choose. If there's only 2 rivals for the hero's affection, it's a Love Triangle.
 * Note that these do not necessarily have to be serious contenders. The situation could shake out to a Official Couple or a Love Triangle situation, with the extra, "beta" characters being Pretty Freeloaders or be genuinely interested—but not to the point of the "real" relationship interests. Many Love Dodecahedron situations in harems turn out to have some of the beta characters having Hidden Depths in the form of outside relationships—a girl who initially seems to be pining for the hero may actually be suffering after losing her husband to illness, or be awaiting her fiancee's return from overseas.
 * Status Quo Is God: You don't have a series if the hero picks a girl and spits it out, so naturally he won't be able to.
 * Accidental Pervert and many of the Comedy of Errors tropes: Misunderstandings are going to move your plot forward, you should stop thinking about avoiding them and start thinking about how to do them well.

Choices, Choices
First things first, you will need to figure out the level of harem-ness. Is it a protagonist with a large number of Pretty Freeloaders and a rapidly less understanding girlfriend? Is it a pair of Childhood Friends both realizing their feelings for the hero at the same time he finally makes progress with the new exchange student? Is it a band manager trying to keep a group of diverse personalities from killing each other?

Does anything get resolved? Are certain characters destined for a bus? Is it Love At First Sight?

Pitfalls
There are good harem stores, and there are bad harem stories. The genre does not work without actual interpersonal conflict. If one character isn't likable, then there's no reasonable struggle, no drama.

While Harem Series have a very classic series of tropes, it's very important not to fall into the standard formula too much, lest you be seen as going through the motions. Status Quo Is God, but pointing this out too much will push your luck with the audience.

Avoid abruptly Cleaning Up Romantic Loose Ends as best you can.

Potential Subversions
There's a reason masculine pronouns have been used so far—flip the genders. Girl with Boy, Boy, Boy, Boy. This is becoming more popular as creators across the world try to defy the Girl Show Ghetto.

Flip the sexuality of the characters. Boy with Boy, Boy, Boy, Boy, or Girl with Girl, Girl, Girl, Girl. A popular gag character is a gay character getting in on the harem against the protagonist's wishes, or joining the Harem not to chase after the protagonist, but to chase after another character in the harem—and this is ALWAYS played up for creep factor—after all, there's No Bisexuals, right? Obvious subversion: Boy with Girl, Girl, Boy, Boy or a Girl torn between the hunky new exchange student and her best female "friend".

The end result of almost all of these series is the characters pairing off with each other, one at a time. The subversion then becomes if the protagonist, or his harem, simply refuse to be shut out by a silly thing like monogamy. Kanokon did this to hilarious effect — Kouta ultimately picks Chizuru but that hardly slows Nozomu down—and in the end, they decide to share him.

A common subtype (based on the first major Deconstruction of this trope, Urusei Yatsura, which ironically came before the Harem Anime really was codified as a trope) is to have the hero be a royal pervert and the "harem" unable to stand him for more than a few minutes at a time—at first. Flipping this, having an asexual character, one who is genuinely not interested in the harem is an interesting subversion, as is the much darker "stalker" type—when the "harem" is all in the protagonist's head, and they are all genuinely not interested. The Harem Anime setup is usually played up for comedy—but it doesn't have to be.

Perhaps the least used subversion would be to not focus on the guy in the middle at all. Try taking a look at the situation from the POV of a girl who has to compete with four or five other girls for someone's affections. What makes this boy so special to her? Is her interest in him really romantic in nature, or she really just a friend who doesn't want to lose him to a girlfriend? What will she do to stand out in his eyes, and most importantly, what will she do if he picks her? What if he doesn't?

A lot of harem animes have the guy finally choosing the Yamato Nadeshiko, the Tsundere, or whoever he met first, which is getting pretty damn predictable. Why not have him choose the brainy chick, the Otaku, the Cool Big Sis, or the gangster girl? Heck, speaking of Tsunderes, how about avoiding Double Standard Abuse (Female on Male)?

Potential Motifs
The Unwanted Harem, unless you're subverting that trope. The standard motif of this series is one "true" pairing, which the hero will not realize until the end. If one of the harem characters (the "one true paring") realizes this before the hero does (and this is becoming more and more standard nowadays) expect lots of Cannot Spit It Out.

Suggested Plots
The Romance Arc, obviously. In addition, everything under Fan Service and Romantic Comedy, only with multiple parings. Eventually the series has to end—the Romantic False Lead might start to make an appearance as some of the tetrinary characters get over the hero, which may or may not go over well.

Generation Xerox is also a type commonly used in fanfiction, but rarely if at all in an actual series: The whole harem thing was resolved a long time ago. The hero made his choice, and everyone's come to terms with that and gone on with their lives, found other loves, and everyone has children of their own... Then Puberty starts to kick in with the new generation, and wouldn't you know it, it's all centered on the Official Couple's child, or the child of another couple, or someone else entirely. Suddenly, the parents see what it was like on the outside of the situation they grew up with. Some may despair, some may laugh, others may see it as a second chance of sorts (especially if there were other matters aside from (or alongside) feelings influencing their participation in the first place): If I couldn't have you, my son will have your daughter.

Set Designer / Location Scout

 * Almost universally, you're going to be looking at young characters, and young characters almost always mean schools, libraries, and the like.
 * You need a house—or dorm, or inn, or apartment complex—that will hold 3-10 people comfortably.
 * A Beach Episode is almost a requirement. A Hot Springs Episode is usually par for the course, as well.
 * Mixing in some other genres—scifi, fantasy, etc—is possible as well, and would definitely affect your location choices.

Costume Designer

 * Transfer Student Uniforms and casual wear that plays up the characters' personality. Fan Service outfits are common as well.

Casting Director

 * See Mahou Sensei Negima as a textbook example of the genre minus (most of) the sexual overtones—the Hero is a child. Just about every Anime girlfriend trope is in here -- not that there's anything wrong with that. You have mysterious foreigners, glasses-wearing girls, slightly chubby girls, genki girls, a Tsundere with a past, a Ojou with a Shotacon complex, pairs of mischievous twins, a schoolgirl lesbian or two, sporty girls, a ghost girl, a vampire Elegant Gothic Lolita, a robot...
 * This should not be considered a typical Harem Anime series, however, as this particular example, outside of casting, was a textbook case of Writer Revolt—the author and artist wanted to do a fighting manga, his publisher wanted a harem manga, and he played along until it was popular enough that he could do a Genre Shift.
 * Your hero is probably going to be an Unlucky Everydude; this can be subverted, however. How about a hero that's The Ace and completely Oblivious to Love? Or worse (for the girls) -- The Ace who also happens to be Invisible to Gaydar?
 * At least one character, most likely the "one true girl" will be a Tsundere who Cannot Spit It Out. A Yandere foil is becoming common as well, played up for a various balance between creep factor and comedy.
 * Standard other female characters include:
 * The Smart Girl (Glasses, short hair, very meek)
 * The Hard-Drinking Party Girl ("American" style characterization, very outgoing, often lustful)
 * The girl he's known since childhood
 * The Token Mini-Moe
 * The Magical Girlfriend (alien, witch, monster-girl, etc)
 * Modern additions include:
 * The Christmas Cake (Often a teacher, often very concerned with the goings on, which she uses to justify her growing attraction to the hero)

The Greats

 * Ranma ½ starts piling on the harem girls—and then the girls gain their own harems. Plays up just about every related trope, despite Word of God saying that Akane and Ranma are the real couple and everyone else is just a distraction. Shipping wars follow this series to this very day.
 * Similarly, Urusei Yatsura was already subverting this trope in the early 80s—with the world's Universe's biggest pervert Ataru Moroboshi trying to intentionally invoke this trope, and failing. Had an odd case of pseudo-Running the Asylum—the fans vastly preferred Lum, who was originally going to be the distraction between the original Official Couple, Ataru and Shinobu.
 * SHUFFLE! was a rare example that ended the Love Dodecahedron before the series did. That didn't end well.
 * Likewise, the rather brutal Deconstruction School Days took this general idea, dashed in a nearly Games Workshop-level of Grimdark, and, well, It Got Worse. Oh God, did it ever get worse. Proof that a Harem Anime doesn't have to be comedy.
 * Kanokon is also a good subversion, with the hero being a near Asexual cute little boy being hounded by two extremely lusty and busty girls.
 * Elfen Lied is what you get when you take a Harem Anime and remove the comedy, replacing it with drama and gore. It's also excellent.
 * Tenchi Muyo! (OVAs 1 and 2) are essentially the most famous harem in the United States, and one of the trope codifiers. They also named one of the more common solutions to the harem problem.
 * Ouran High School Host Club is a Stealth Parody of Shoujo Romantic Comedy stories, but specifically aims towards Reverse Harem. Oh, and it has plot behind the absurd amount of comedy.

Contested
Some examples that worth the look so you can SEE the pros and cons, in this case, Your Mileage May Vary.
 * Rosario + Vampire: Better Than It Sounds, despite all you heard about them is...Fanservice, or Loads of them. Pros: Good for making the Harem aspect and Interspecies Romance sadly serious and fleshed out, Cons: Too much fanservice, especially the Anime.
 * The Wallflower involves people specifically trying to invoke the Reverse Harem version of this, all in the hope that having a Harem will cause the not feminine at all main character to girl up. Doesn't really work.
 * Though one must point out that it's not neccessarily that she's unfeminine. It's just that she's a Nightmare Fetishist who looks like a Stringy-Haired Ghost Girl. Once you get past her love of all things gore and horror and apparent allergy towards all things (conventionally) beautiful, she's actually quite the Yamato Nadeshiko. (Also probably a reason the reverse harem doesn't really work in making her more 'feminine.')

The Epic Fails

 * Tenchi Muyo! (OVA 3) shows that harem stories that are filled with My Kung Fu Is Stronger Than Yours can dilute the plot to the point of pointlessness, and the addition of Mary Sues to the cast never helps.
 * Tenchi Muyo! GXP also shows that trying to stay Strictly Formula is fine, shows still need some form of extra oomph to push it up from "mediocre," to "watchable." As with OVA 3, this Tenchi series seemed to have the harem aspect just because everyone expects a Tenchi series to have a harem (never do this), and when harem antics are something you just endure so you can watch the ever wacky antics of Seriyo Tennan, you've messed up.