Yes, it can be. Sirius Black has a complex character with his own backstory, and when incorporating him into Hermione - centric fanfiction, it's tough to balance his personality traits like his recklessness and loyalty with Hermione's studious and rule - following nature. Their different personalities and the existing canon storylines can make it a difficult task to create a believable and engaging plot.
Well, it depends. If the writer really understands both characters well, it might not be that hard. However, Sirius Black comes from a different generation and has a lot of baggage from his past, like being in Azkaban. Hermione, on the other hand, is very much a product of her Hogwarts education. So, to make their interactions seem natural in a fanfiction, one has to be careful about how they meet, what they talk about, and how they influence each other. It's not an easy feat, but not impossible either.
Definitely. Sirius Black is a character who has seen a great deal of darkness and has a rather wild side to him. Hermione is a character who values knowledge and order. In fanfiction, if you want to bring them together, you need to find a common ground. Maybe it could be their shared love for Harry, or their fight against the Dark Arts. But still, making their relationship work in a story requires a lot of thought. You need to think about how Sirius would react to Hermione's intelligence and how Hermione would deal with Sirius's unpredictable nature. All these factors contribute to the difficulty of writing Sirius Black in Hermione fanfiction.
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Chapter 334, "Hanqiong's Seven Divisions, Moao Mountain, Beishuo Revisited 5", is the clearest early answer because it turns Hong Yuru's situation into a concrete plot event. A useful checkpoint is the way the scene starts with According to Fan Kui, let's first explore northward together to see... and follows through with Beining Mountain, seven camps, judging by this kid's cultivation and....
Chapter 309, "Then Come Die with Me!", is the clearest early answer because it turns Chixia Village's situation into a concrete plot event. It opens with In the dim and damp underground room, only a single incandescent bulb... and closes on Hahahaha, you want to kill me and become the true Gu Yu?.
Chapter 345, "Luo Ming, Mirror Valley Defense Commander, Beast Tide, Great Xia's 6 Armies", is the clearest early answer because it turns Redwood Ridge's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Great Xia, Year Seven, September Ninth, the latter half of the night... and follows through with In the first half of last year, Li Baihe, Xu Kang, and Shang Ping....
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Chapter 281, "Zhao Lang, Are You Willing to Take a Gamble?", is the clearest early answer because it turns Gamble's situation into a concrete plot event.
Chapter 172, "Shang Shaojing is Here Too?!", is the clearest early answer because it turns Sister Li's situation into a concrete plot event. It opens with Not only Shu Yan, but the entire internet was shocked when they saw... and closes on Where's the chaotic scene I was anticipating?.
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