Magical girlfriend

A magical girlfriend (also referred to as exotic girlfriend, supernatural lover, or nonhuman woman) is a female (or male, in rare cases) often associated with romantic comedy anime and manga series, and is sometimes considered a genre of its own, or as the leading lady of the "fantastic romance" genre, which combines the fantasy and romance genres.

As Thomas LaMarre states, "Anime fans become familiar with a whole range of female figures that are either not really human (robots, aliens, deities, animals), or that possess extra-human powers of some kind or another (from cyborg enhancements to magical or psychic abilities), which take them beyond the merely human woman."

Magical girlfriends can be one or many in a single series (always attached to the male lead). Because of the tendency for rivals to appear even when there is one female lead and because of the unnatural gender balance among the cast, magical girlfriend comedies are often conflated with harem comedies. A good example of this conflation is Oh My Goddess! which is "one of the prototypical 'harem' titles" despite the short-lived nature of most of the romantic rivalries.

Often series in the genre start with the male lead encountering the female lead either by pure chance or by an unusual event, after which the female lead somehow becomes bound or otherwise dependent upon him, often forcing a situation of cohabitation. In many cases, this situation is repeated with other characters (Tenchi Muyo!), overlapping with the harem genre. However the male lead is often inexperienced with women despite typically being a "nice guy". This situation often prevents the relationship from advancing beyond a platonic level throughout most of the series, as an ideal girlfriend doesn't come on strong herself and is generally passive in the relationship.

In parodies, the character may be "too young" (i.e. Nakahito Kagura in Steel Angel Kurumi; Negi Springfield in Mahou Sensei Negima!) or otherwise have a more rational, ambivalent attitude towards women. A famous early reversal of the cliche occurs with the overtly lecherous Ataru Moroboshi of Urusei Yatsura), who is simply uninterested in monogamous relationships despite the fact few women besides his romantically-aggressive alien girlfriend find him attractive.

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Wikipedia