Set in the modern age, the story is about Rokujo Miharu, who just wanted to live a normal life and inherit a restaurant. At the moment, his biggest problem was the constant pestering from Kouichi Aizawa and Thobari Kumohira, who started a Nindō (忍道, Nindō? lit. "Way of the Ninja") Club. Miharu wanted nothing to do with "ninjas" and turns them down every time. But soon, he is attacked by an actual group of ninjas and is protected by Kouichi and Kumohira. There, Miharu learns of the hidden ninja world Nabari, the roles of his classmate and teacher in that world, and of the hijutsu Shinrabanshō (森羅万象, Shinrabanshō? lit. "all things in nature") within him. The hijutsu, containing all the world's knowledge, is sorely coveted after in Nabari. And because of that, Miharu cannot return to his normal life. He must become the "Ruler of Nabari" to survive.
This manga is awesome. It might get compared to Naruto because of some similarities, but they're two completely different manga, and this one has the upper hand. It has a likeable main character, better characters in general, a better storyline and plot, and everything. And I think what Miharu has trapped in him is personally more interesting than a demon fox, but that's just me. Again to the Naruto comparison... my acquaintance said Nabari was boring and he loves Naruto, and although I don't AGREE, I can understand as sometimes it has more action I'd think. Maybe that's why Nabari is so much better to me because it has more... depth.
Don't take my word for it, go read it, at least give it a chance, especially if you like ninjas.