Toaru Majutsu no Index - Volume 17, Prologue

In the continent of Chang’an humans had lived as livestock and slaves to the Primordial Beasts. These beasts were ferocious, bloodthirsty and overwhelmingly powerful, but even so, the humans managed to prevail in the face of despair.

When The Cute Kunoichis Spied on Their Teacher's Secret is a light novel written by Kazuma Kamachi and illustrated by Ryuushi Tajima.

The story takes place in a world where Japan never ended their isolationist phase, and agents from foreign powers are always threatening to steal the country's advanced technology. In order to combat this threat there has been a resurgence of ninjas that use Strategic Martial Arts, techniques that combine cutting-edge modern technology with a traditional foundation of martial arts and ninjutsu. The story follows Souha Sugiyado, a 17-year old ninja instructor and former ninja prodigy who was forced to retire from active duty by the wounds he suffered in his last mission. Souha's four students are all kunoichi who have all gained the rank of Elite Ninja, the highest official rank available to ninja. However, one day two Shogunate ninja approach him with the news that his four students have gone rogue and have stolen a portable modular nuclear reactor, and thus they ask for his help in bringing his students to justice.

This is a world where humans, demons and mysterious beasts coexist. Humans cultivate mysterious qi. Demons cultivate corporeal bodies. Mysterious beasts cultivate soul perception. A legend says that in the middle of an endless rainforest, there are extremely powerful existences; they are called demon kings. Some demon kings have a tyrannical corporeal body, some are experts in illusions. Some demon kings are proficient in magic, some can even move mountains. Some demon kings are able to sense things thousands of miles away. These demon kings rarely appear in the human world. Even if they emerge in the human world, they would reincarnate in human form; assimilating with mankind while seeking to breakthrough realms…….

Xu Yiren, who has 300,000 fans, scolded Song Tianmei, a new traffic flower with more than 5 million fans, on Weibo: “Who in China doesn’t know that Gu Yu is your backstage!” People are sitting at home, and the pot is coming from the sky.

Gu Yu: “Excuse me?”

Three months later, Gu Yu put his hand on Xu Yiren’s side and said softly, “I have never been the backstage of anyone in my life, but from today onwards, I will be your backstage.”

- Description from Novelupdates