 If you liked
Suzumiya Haruhi no Yuuutsu
|
 ...then you might like
Yakushiji Ryouko no Kaiki Jikenbo
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In these animes, the lead guy is often being force by the lead girl to follow her in her adventures. The lead girls have a very lively and mischievous personality, while the guys have a more passive and introvert personality. Both animes deal with some kind of supernatural phenomena, and the main characters try to solve those.