Plot (taken from MAL)
Silent, apathetic, yet mischievous, 14-year-old Rokujou Miharu is the bearer of the hijutsu, "Shinrabanshou," a powerful technique many ninja clans desire to possess to become the ruler of Nabari. Fellow classmate Kouichi and his English teacher Kumohira are both secretly Banten clan ninjas, pledging themselves to protect Miharu from his many attackers. Keeping apathetic, Miharu attempts to reject their invitation to join their ninja "club." However, after numerous attacks, he finds no choice but to join their group as a means for his survival. Slowly, Miharu takes a step closer to becoming the ruler of Nabari.
Thoughts
Am I perhaps blinded by nostalgia?? I dunno, but this series is just too special to me for it to not be one of my favorites. I think it was one of the first animes I watched. Similar to Princess Tutu, I watched this when I was but a wee lad and rediscovered it later in middle school. During middle school, this was basically a comfort show for me. I don't even know how many times I rewatched it. But enough of my nostalgic rambling...
I don't know how to describe it, but the show has this certain charm to it. The character dynamics are A+ (especially Miharu and Yoite but I'll get more into that on my otp page). I love Miharu's personality. He has this power but is too apathetic to even have anything he wants. This sets him up to develop and decide things for himself. My main gripe with this series is that despite it ending cleanly on a major plot point, it's bascially a 'read the manga' ending if you want to see what happens next.