 If you liked
IS: Infinite Stratos 2 - World Purge-hen
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 ...then you might like
Nisekoi: OVA
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Both shows are OVAs that were released outside of the original series. In essence, they both build off the harem genre to some degree. They also share practically the same plot (at least the first half of Nisekoi: OVA does): each of the main female characters have some kind of idealized dream involving the main male character.