It really varies. Some manga have characters who can keep secrets well, while in others, secrets are spilled easily. It all depends on the story's context and the personalities of the characters.
You can search for 'Keep a Mummy' on the Crunchyroll website or app and start watching if it's available. Just make sure you have a subscription if needed.
It's not a straightforward yes or no. Some creators have full rights, while others may have to give up certain rights depending on the terms agreed upon when their work is published or adapted.
Well, she could make it more difficult at times. Her constant moaning might be a distraction for Harry when he's trying to study or think in the bathroom. But on the other hand, she could also be a source of useful information. For example, if there's something strange going on in the bathroom or nearby, she'd probably be the first to know.
Yes, there are many 'Naruto Kurenai' fanfictions that focus on various aspects other than inappropriate content. For example, some might explore their friendship, or their roles in different missions within the Naruto universe. There are also fanfictions that develop their characters in new and interesting ways, such as Kurenai teaching Naruto some special jutsu or them working together to solve a mystery in the Hidden Leaf Village.