Kami no gyakuten:The yamato hero - Chapter 14: Cave of Seiryu Clan

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.

The devil would love you only in his own way: “Remember, don’t look at me, don’t hold me, and don’t kiss me! Turn your face away, as long as you lie down obediently and quietly! ” Just lie down obediently? What did he take her for? An inflatable wife?

- Description from Novelupdates

“Obtaining the topmost degree of talent in sword arts in the world requires giving up 72 years of lifespan, which leaves you with only five more years of your life. At the same time, you will never be able to feel love, kinship, and friendship, and you’ll end up leading a lonely life until your death, unable to procreate, or to have any descendants.

“From now onwards, everything related to happiness in the human world shall no longer be of your concern. Are you willing to accept this?”

“Hahahaha, I’m already alone bereft of all support, my hopes dashed to pieces, shouldering only absolutely irreconcilable grudge and hatred, why would I disagree? Why would I not want it? I couldn’t ask for anything better!!”

His sword sweeps across the Divine Continent for seven days and nights, moving 90,000 miles through the starry skies, unhindered.

He slays saints and buddhas in Heaven, slaughters demons and devils in Hell, sweeping away all the grievances in his heart!

- Description from Novelupdates

I don’t need any deep relationships. I have no desire for a girlfriend, and I only require one friend who holds any value to me. Ever since I threw out my youth for the sake of efficiency, there is one person who keeps entering the bedroom of Ooboshi Akiteru. She’s neither my little sister nor my friend. She’s nothing more than a bothersome, annoying Kouhai, as well as my friend’s little sister: Kohinata Iroha.

“Senpai, let’s go on a date~! Did you think I’d say that~?”

Rather than blood, it seems like energy drinks run through her veins. She keeps occupying my bed, and she tries her best to seduce me with whatever method she can play to her favor. She’s a girl who’s constantly annoying and obnoxious around me. Even though I’m busy all day long, she doesn’t care.

And in case you’re wondering why all these envious gazes are directed at me, it’s because Iroha is actually really popular. She’s an honor student at our school with top grades to boot, and she’s known for being kind and proper to anyone she meets.

…Hey now, why are you only so annoying when you’re around me?