They are not common. Literature usually gravitates towards topics that have broader appeal. Hypnotized little sister stories are rather niche. While there might be some short stories or even parts of novels where hypnosis is involved, it's not a typical plot device when it comes to a little sister character. It might be more likely to find in some experimental or indie literature pieces.
It is completely inappropriate. Erotic content has no place in proper literature or general consumption. It objectifies and disrespects others, and can have a negative impact on one's mental state and values. We should stay away from such materials.
The story might start with the sister's best friend being hypnotized during a strange eclipse. She starts acting out of character and doing things that are not normal. The sister realizes something is wrong and decides to seek help from a local wise woman. The wise woman tells her that the hypnosis is related to an ancient curse that was placed on their land long ago. To break the curse, they need to find three magical stones hidden in different parts of the village. The sister and some of her other friends then start a quest to find these stones. It's a race against time as the hypnosis on the best friend is getting stronger, and they must work together to save her.
One possible story could be that the sister's best friend discovers she has a special power to enter people's dreams. She accidentally hypnotizes the sister while trying to show off this power. In the hypnotized state, the sister reveals her deepest secrets and desires. The best friend then has to figure out how to reverse the hypnosis without causing any harm or revealing the secrets to others.
A simple story could be that the sister's best friend has a magic pendant. When she touches it while looking at the sister, it hypnotizes her. The sister then starts acting like a character from a fairytale. The best friend has to use her wits and some other magical items she finds to break the spell. Maybe she has to go on a quest to find a special flower that can reverse the hypnosis.
There could be a story where a little sister is hypnotized by accident. For example, she watches a strange, swirling pattern on an old TV screen that has some sort of hypnotic effect. As a result, she starts acting in a very different way. She might start speaking in a language she doesn't know or be able to do amazing physical feats like balance on one foot for a really long time. But then her older brother or sister has to figure out how to snap her out of it.
Sure. Once there were two sisters. The older sister was very good at painting. She decided to teach her younger sister how to paint. They set up their easels in the garden. The younger sister was a bit clumsy at first, but with the patient guidance of the older sister, she gradually got the hang of it. They painted the beautiful flowers and the blue sky, and that day was filled with laughter and the joy of sisterly bonding.
One possible moral could be the importance of being vigilant. In the story, if the sister's best friend was hypnotized because she let her guard down, it shows that we should always be aware of our surroundings and not be too trusting of strange things. For example, if she was hypnotized by a mysterious object, it teaches us to be cautious.
I recommend the novel," I was reborn after being possessed by the Book Piercer." The female protagonist in the story, Gu Qingwan, was supposed to be the female protagonist of a Mary Sue cultivation world, but she was possessed by the book transmigrator and became the puppet of the enemy. She was later reborn and returned to the time before it happened. She grasped everything and revealed the book girl's conspiracy. This novel matched the theme of the female protagonist being possessed by hypnosis.