There's a volume on the manga that is almost similar to Love Hina
Just read on the middle part of volume 15 of Suzuka (if there will be available for English translation and license). There, Yamato made a promise to his childhood friend, Saki that they should go to Tokyo University together and made them a pinky swear. But then, Suzuka had a recommendation from Seijoudai that might broke his promise to his childhood friend, Saki. And the rest should read it all, and no additional spoiler for now. Man, I wish there should be another season on the anime series, soon, because the 1st one was just a half of the manga itself.
Our world becomes paranoid after 10,000 B.C.