Nanagenme wa Ninja Shugyou desu!

Shino Hattori, a sheltered young lady from Iga City, never fits in at school. She thinks making friends is just a waste of time, so she spends each day alone—until she finds a strange coded note in her desk:
"Meet me behind the gym after class."
Curious despite herself, Shino goes...and meets Kanna Ueno, a girl who wants to become a ninja.
Kanna insists they do "ninja training" together—basically ninja pretend play—but Shino immediately refuses.
But Kanna won't take no for an answer. Armed with her "ninjutsu" (or something like it), she drags Shino into a whirlwind of trouble...!?

(Source: Kadokawa, translated)