if i have to summarize this manga series in a few words, it would be "the greatest harem romance manga series ever."
although it does not have comedy like Love Hina or action like Negima, this series' ability to actually form a working relationship between the protagonist and the heroine makes it one of the most interesting harem series to read.
no summary can be made becuz that will be spoiling it. ill link a animenewsnetwork link to it so you can read the submitted summary for getting into this series. there is an anime series based on it, but it is inconclusive unlike the manga series, so i STRONGLY suggest you to read. its okay to watch it too, but make sure you read the series. it is really good.
http://www.animenewsnetwork.com/encyclopedia/manga.php?id=2581