Harem anime

Harem anime is a fan-term, usually used prejoratively, to describe a plot concept rather than a genre, although most are in the romantic comedy genre. Presumably they are a protect of adaptations from ren'ai (dating simulation games) where writers intended to please fans of each character by giving them equal importance with an anime series.

A few series aimed towards girls contain vaguely harem-like elements (albeit with inverted genders when appropriate) including Fruits Basket and most famously Fushigi Yugi.

They generally consist of a few key concepts. The prototypical harem anime usually features:

A lead male, sometimes the lone boy in the series, sometimes with a plain appearance or more introverted compared to other characters. Although not always cofortable around women, his saving graces are an immense capcity for empathy and understanding with other more unusual charcters, although his dislike of upsetting people sometimes makes him appear meek or wishy- washy (which often frustrates American audiences). He is also considered non-threatening and harmless for the most part, so the girls take a relaxed attitude around him.
A normal (usually two) 'friend' of the lead, also usually male. Sometimes the opposite of the male lead (extremely handsome, rich, but more judgemental) He usually laments about his own shortcomings and envy of the Male Lead's apparent lifestyle, much to Male Lead's annoyance. He is sometimes a ineffectual rival to the Lead.
Several girls, usually of common anime character archetypes designed to appeal to the audience rather than the lead. As the term implies the number of girls is usually at least three or four instead of two (See love triangle) who usually find something appealing about the lead, to varying degrees. In more slapstick Love Comedies, each girl often has quirks which make her seem unusual, offensive, or otherwise best avoided to more judgemental 'normies' outside the group.
- Lead Girl: For shows that 'pick' an explicit co-star, the girl the main male lead will eventually end up with. She is usually the most 'average' of the girls.
- The Other Girl: Usually Lead Girl's rival in regards to the plot, although they may be good friends. Mostly used when an explicit pairing is being lead up to in the series.
- Traditional Girl: These can include yamato nadeshiko 'housewife' types (who are almost always leads in that case) or overly serious samurai or miko types. Sometimes the latter type is paranoid of men, and enjoys the company of the lead because he is harmeless and nonthreatening.
- Tomboy: Self-explanitory. Ironically, this personality is also associated with confident, party-going, slightly deviant Sexy Types. Her attraction, if any, to the lead is usually of harmless Big Sister friendship or only passing attraction.
- Little Sister: Usually not an ACTUAL little sister, this character is often very intelligent for age, has personality traits of the Male Lead, or on the flip side, incredibly shy and bumbling. The lead provides her a big brother outlet or an non-threatening crush object. She is the youngest of the group and sometimes lacks another child around for normal companionship.
The 'Nanny': This is usually an adult character who (ostensibly) is a final authority figure of the group, usually a distant relative, senior citizen, or other good-natured and non-critical advisor.

Very few popular anime are strict harem series although many use the concept loosely, and considering it's mostly used negatively, it's a hotly debated distinction. Series that seem like harem anime but lack explicit romantic concepts are likely simple bishoujo (shows with cute girls) series. Note that like harem anime, bishoujo is not really a genre so much as an easily recognized design concept.

Harem anime is considered one of anime's more blatant vicarious concepts. One reason they often lack specific closure is many involve male leads who lack a strict presence of family, and thus the cast provides a makeshift family dynamic. Another is the makeup of the characters often seems uninspired or downright milquetoast as series cannibalize each other.

Examples:

Tenchi Muyo, especially the later television series, contains most of the common elements, and although certianly not the first, is considered by many American fan to be the protypical (or at least famous) harem anime
Steel Angel Kurumi 2 contains elements, although a major difference is all the characters, INCLUDING the lead, are women.
Happy Lesson has no romantic elements at all. INstead the emotional element is that of parents as five characters serve as the main character's 'mother' (much to his confusion and annoyance.)
Love Hina another famous series which in younger audiences supplanted the Typical Harem Anime title from Tenchi. While not a harem anime, it uses humor and satire to poke fun at harem anime (the lead female is even a parody of the Average Lead Girl in ren'ai games)
Ai Yori Aoshi is a recent anime going for a dual concept, both magical girlfriend and psuedo-harem anime. Unusally, the lead is a fairly well-adjusted & social character (even around girls) despite crushing former abuse. AYA escapes the harem anime moinker because of the lead's early explicit devotion to the Lead Female, although they do live with a cast of other girls whom they must keep the relationship a secret from.
Sister Princess and Hanaukyo Maids are generally considered to be a true harem anime, although the later is quite tongue-in-cheek.