Instead of Checking In Regularly: I Hide And Cultivate In The Monster-quelling Tower And Become Invincible - Chapter 606: Thunder Sound Tower in the Far West

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.

“monarch of entropy” introduces a cosmic entity of immense power, whose eternal existence was once defined by passive observation. Everything changes when a surprising connection ignites a spark of curiosity and a yearning for interaction. As this King explores his evolving desires, his colossal abilities begin to influence realities on an unimaginable scale. This is the story of a powerful ruler's journey from detached observer to active participant, where every decision, no matter how small or whimsical, creates ripple effects across the multiverse, leading to a series of grand, and sometimes inconvenient, adventures.

Thanks to the Goddess, he was reincarnated into nobility!　That should have been great―― but the skill he got, 【Toxin Decomposition EX】 was simply too plain, and he was made fun of everyday at home……

A teenager named Evan Mason was reincarnated into the magical world of Harry Potter and goes to school at Hogwarts!
With only his knowledge of the future and great talent for magic, he takes the path towards the top of the magic world, only to realize that ever step he took, changed everything!

- Description from Novelupdates