Guardian Ninja Mamoru(2006)

Guardian Ninja Mamoru is an anime series following Kagemori, a nerdy, unassuming student who conceals a deadly secret: he's a master ninja sworn to protect the Konnyaku family. For four centuries, Kagemori's clan has guarded the Konnyakus in the shadows. His primary charge is Yuuna, the family's spirited young daughter, a responsibility he's held since their kindergarten days. Whenever Yuuna stumbles into danger—and she often does—Mamoru materializes from the darkness to save her, his true identity hidden behind thick glasses and an awkward exterior. The series blends comedy with action as Mamoru balances his ordinary school life against his extraordinary duty, constantly rushing to Yuuna's rescue while maintaining his cover as just another clumsy, forgettable classmate.