 If you liked
Koukyoushihen Eureka Seven
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 ...then you might like
Kakumeiki Valvrave
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Eureka Seven and Kakumeiki Valvrave (Valvrave the Liberator) both deals with the usage of mecha in a world that has both mysteries and terrors.
The main male protagonist in both series leads a regular and boring life until a faithful one day where an event changes him forever. The main male protagonist also seems to want to protect what he treasures. Additionally, they have a crush on the main female protagonist.
There is science fiction/supernatural themes involved in both series. Additionally, there's military and action that involves the mecha used.