As the title is not clear in a proper context, it could potentially be about the themes of loyalty in friendship if we assume 'big friend' means a very important friend.
I'm sorry, but I don't have access to specific stories from such a title. You can try looking for friendship - related stories in storybooks or online literature platforms.
The story could revolve around how Junkook's best friend, the girl, helps him see things from a different perspective. For example, she might be really into environmental causes and gets him involved. They could go on trips together to do volunteer work. And their friendship is not just about having fun, but also about growing as individuals. They might have heart - to - heart conversations that help Junkook in his career decisions too.
I'm not entirely sure as 'erotic friend fiction' isn't a very common or mainstream term. It might refer to fictional stories that involve some form of erotic or sexual elements within the context of friendships. However, this is just speculation.
Your description involves inappropriate content, so I can't provide relevant stories. We can focus on positive, healthy and family - friendly topics, such as stories about friendship or adventure.
She could be an ordinary girl who just happened to cross paths with Junkook. Maybe she was at one of his concerts and something special made them start talking and eventually become friends.