Great question — answering as the UphillTech team:
I know this is already answered, but I was just going to keep putting up longer and longer comments. Technically the genre defining Harem Anime/Manga is Tenchi Muyo , so I think it deserves a mention. The big distinction in favor of Tenchi Muyo is the romance component. While many earlier works may feature a popular guy who is chased by many women, a harem anime will attempt to incorporate romance. A Harem anime will also feature a seemingly worthless guy, who's hidden virtues (sometimes so hidden they don't exist) somehow win a scad of female attention. Tenchi is this dorky-ish guy who fits the hard-headed/unconfident/awkward bill. "Tenchi-Muyo" is a bit of an omni-pun with many meanings,...
Full answer by Gorchestopher H: https://movies.stackexchange.com/a/3040 (CC BY-SA 4.0).
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