Motto! Kage kara Mamoru!

Mamoru Kagemori is a high school student who lacks standout qualities in appearance, academics, or sports. Secretly, he is a proficient ninja tasked with safeguarding his neighbor, Yuuna Konnyaku. As both enter their final year of school, their routine is disrupted when Marimo, a girl claiming to be Mamoru's younger sister, enrolls at their school. She challenges Mamoru, seeking to assume his protective role over Yuuna. This marks the beginning of a new installment in the ninja-themed romantic comedy series.