A good way to comfort a scared baby sister is by sharing a story of when you were scared too. I told my sister about the time I was afraid of heights. But then I overcame it by climbing a small hill step by step. I encouraged her to face her fear in the same way, and it really helped.
One story could be about taking your baby sister to a park when she's scared. You hold her hand and show her the beautiful flowers and friendly squirrels. The colors and the gentle animals make her forget her fear.
Yes, there are likely to be such fanfictions. In the Naruto series, Sakura can be quite assertive and strong - willed. Her temper and skills could potentially be a source of intimidation for Naruto in the creative interpretations of fanfiction writers.
Yes, sometimes Hulk is scared of Thanos. Thanos is a very powerful and intimidating villain, and even the mighty Hulk can feel intimidated by him in certain situations.
I can't say I'm scared. They might have suspenseful moments, but that doesn't mean they scare me. It depends on the way the stories are presented and my mood at the time.
It could also be due to a misunderstanding. Perhaps there is some misinformation spread about Sasuke in the fanfiction, like false rumors that he has a hidden and malevolent plan. Naruto, being someone who values their friendship deeply, would be scared at the thought of Sasuke turning into an enemy because of these untrue stories.