A harem includes three or more characters who potentially show romantic interest in a male protagonist. The sex, gender, or orientation of the harem members is irrelevant as long as they exclusively, or at least primarily, are vying for the affections of the same individual - who may or may not reciprocate towards one, several, or none of these romantic rivals.
These anime feature young, generally school-aged girls as defenders of love, life, and justice. They typically stumble upon the source of a magical power, or are granted one by allies that are aware of evil forces on the rise. Often by using a special item or with the help of a magical familiar, these characters are able to transform into an alter-ego ready to cause mischief or fight their foes.
Mystery anime focus on unresolved questions, and the efforts of characters to discover the answers to them. Whether curious and deadly events are afoot, or some part of the world itself is strange or inexplicable, or someone's past or identity seems strangely shrouded, these characters are set on learning the truth.