It could also be related to a prophecy or a pre - determined fate in the fanfic's plot. There might be some kind of dark prophecy that says Kawaki has to kill Naruto to prevent a greater evil. Or perhaps Kawaki is being controlled by an external force that has a vendetta against Naruto and uses Kawaki as a tool to carry out the murder.
Kawaki makes his appearance in Boruto manga at a specific point, but I can't recall exactly. You might want to check the official manga sources for the precise chapter.
In this kind of fanfiction, Naruto might teach Kawaki about the values of the Hidden Leaf Village. Maybe he'd show Kawaki how to control his powers better. For example, Naruto could take Kawaki on training sessions similar to the ones he had with Jiraiya.
Kawaki might resist Naruto's teachings at first. Since he has his own way of doing things, adapting to Naruto's values and training methods could be difficult. Also, the village might not fully accept Kawaki right away, and Naruto would have to fight for Kawaki to be accepted, which is a big challenge.
Well, it's hard to define the 'best' as it depends on personal taste. But 'Sasunaru in Konoha: The Unspoken Promise' is quite popular. It focuses on the small, unspoken moments between Sasuke and Naruto within Konoha. It's a very character - driven story that really makes you feel the depth of their relationship. Also, some fanfictions that combine action and their relationship in Konoha, like 'Sasunaru: Defending Konoha', are also very engaging.
Since I don't have access to the specific 'sasunaru lemon hard fanfic', it's hard to be exact. But in the world of fanfiction, 'Sasunaru' is likely about the relationship between Sasuke and Naruto from a particular fandom. The 'lemon hard' part is a bit more ambiguous. It might mean that the story has a strong focus on their relationship in a more passionate or intense way, perhaps with a lot of emotional drama and romantic or even slightly more mature content, but again, this is all speculation without reading the actual fanfic.
Well, 'sasunaru' might refer to a relationship between Sasuke and Naruto in some fan-made concepts. 'Anti Sakura' could imply that the fanfic is against the character Sakura. It might involve storylines where Sasuke and Naruto have a special bond or story that goes against Sakura's role in the original work, perhaps emphasizing Sasuke and Naruto's relationship more while downplaying Sakura.
One great sasunaru oneshot love fanfiction is 'A Moment in Time'. It beautifully captures the intense connection between Sasuke and Naruto. The story focuses on a single day where they finally admit their feelings for each other, with vivid descriptions of their emotions and the setting.