 If you liked
Zero no Tsukaima
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 ...then you might like
Maoyuu Maou Yuusha
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The main characters are complete opposites, but are bound by a contract and end up working together for a certain goal. Also, both are romance, but a frustrating "love triangle" happens between the main male character, the main female character and a close friend of the male character. (Harem) Both main male protagonists are blue haired and wield swords. Also a similar feel and atmosphere of both of the animes, and great (but frustrating romance) and stories.