One possible fanfiction could be about an older brother who has to take care of his little brother and deal with the diaper - changing tasks. Maybe he initially finds it gross but then grows to understand it as a part of his responsibility and a sign of his love for his younger sibling.
This is a rather unusual situation in most cultures. However, in a make - believe or very young children's play scenario, one could imagine a story where a little brother, perhaps in a game of 'pretend family', tries to diaper his older sister's doll as if it were his sister. But in real - life, this goes against typical social norms.
In some family - centered stories, the little sister is really into girly things like tea parties. She convinces her older brother to participate. She makes him wear a crown and a cape, and they have a 'royal' tea party. Through this, the brother is feminized as he takes part in an activity that is often seen as more suitable for girls. He might even start to enjoy it and become more open to 'feminine' activities in general.
A fanfiction could focus on an older brother who discovers a special power in his little brother's diapers. For example, the diapers might have some magical properties that only the older brother can detect. This would lead to a series of adventures as they try to figure out the origin and purpose of this strange phenomenon.
No. In most cultures, there are no such references as it goes against the norms of age and family roles. Cultural norms usually emphasize the older sibling's more responsible and independent role.
Another reason could be that she doesn't fully understand how her actions affect her brother. She might think it's all in good fun, like when she teases him about his appearance or his hobbies. But to the brother, it can be really hurtful. She may not have developed enough empathy yet to realize that she's being a bully.
In a story, the little sister might be in charge of deciding what the family has for dinner when the parents are out. She forces her older brother to help her cook her favorite meal by threatening to tell their parents he was mean to her earlier. She bosses him around in the kitchen, making him do all the chopping and stirring while she supervises.
Here's an interesting one. The little sister was sissy in that she was afraid of heights. The older brother wanted to help her overcome this fear. He took her to a small cliff and climbed down first, then called her to follow. He supported her all the way, and after that, she was less afraid of heights. This story shows the bond between them.
One story could be that the older brother ate the last piece of cake that was meant for their mother's birthday. So, the little sister made him clean the whole kitchen as punishment. She supervised him closely, making sure he scrubbed every corner of the counter and washed all the dishes thoroughly.
In some stories, the older sister encourages the little brother to pursue his dreams. For instance, if he wants to be an artist, she gets him art supplies and takes him to local art shows. This way, she supports his aspirations and helps him grow.