There are multiple negative consequences. Firstly, it can severely damage her innocence. A little sister should be in a pure environment, and erotic stories will taint that. Secondly, it can lead to psychological problems like anxiety or inappropriate behavior. She may not know how to handle this new and inappropriate knowledge. Thirdly, it can affect her family relationships as this is something that should not be introduced into a family environment.
No, it is not appropriate at all. Incestuous themes are considered unethical and not acceptable in most societies. Such content is also against moral and family values.
It is completely unethical. Forcing any form of inappropriate or sexual behavior, even in the context of a story, violates basic principles of respect, consent, and human dignity. No one should be made to engage in any such demeaning act in any situation, real or fictional.
One important tip is to use positive reinforcement. For example, if you're teaching her to suck through a straw, when she does it right, give her a small treat or lots of praise. Another thing is to choose the right equipment. A straw with a soft tip might be more comfortable for her. Also, make sure the drink you use is something she likes so she'll be more motivated to learn.
Teaching a younger sister any skill should be done in a positive and appropriate way. If it's about teaching her to suck on a straw, for example, you can start by getting a colorful and easy - to - use straw. Show her how you put your lips around it gently and suck. Let her practice with a fun drink like a fruit smoothie. Encourage her and be patient as she tries to get the hang of it.
Well, it could be that some people find the content too explicit or lacking in depth. Maybe the storylines are weak or the characters aren't well-developed.