One author that comes to mind is someone who goes by the pen name 'ShisuiLover123'. They have written several shisui fanfictions that are really popular. Their stories often have great character development, not just for Shisui but for the other characters in the story as well. Another good author is 'UchihaFanatic'. They tend to write shisui fanfictions that are set in unique and interesting alternate universes, which gives a fresh take on the character. But again, it really depends on what you're looking for in a fanfiction.
There could also be other supporting characters. For instance, Naruto or Sasuke might make appearances in the fanfiction. Naruto could be a friend who offers his unwavering support to Sakura in her adventures with Shisui. Sasuke, as another Uchiha, might have some sort of connection or conflict related to Shisui's actions or decisions in the story.
There are quite a few good writers out there. One way to find them is to search for fanfiction communities dedicated to Naruto (since these characters are from Naruto). In these communities, people often recommend their favorite writers. Some writers are known for their in - depth characterizations of Itachi, Sakura and Shisui. They make the characters feel real and add new dimensions to their relationships. You might also want to follow some fanfiction blogs on Tumblr that often share and promote great fanfictions about these characters.
The Akatsuki could still be the main antagonists. Since Naruto is being trained by Shisui, they would see Naruto as an even greater threat. His new skills under Shisui's training could put their plans at risk. For example, if Naruto becomes better at stealth and infiltration, he could disrupt their operations more effectively.
Another possible antagonist could be a rogue Uchiha. One who didn't agree with Shisui's views on peace. This rogue Uchiha could see Naruto as an outsider interfering with Uchiha matters and Shisui as a traitor for teaming up with Naruto. So they set out to disrupt their partnership and cause chaos in the village.
I'm not sure who the author of this fanfiction is. There are so many fanfiction writers out there, and without more context or searching on specific fanfiction platforms, it's hard to tell.
Liu Shisui and Liu Ci were two different people. Liu Shisui was a character in the " The Great Path Toward Heaven ", and he was Jing Jiu's disciple, who belonged to the Green Mountain Sect. He was described as intelligent, kind, and had a determined temperament. Liu Ci was the Sect Master of the Green Mountain Sect, and was called the Immortal Liu Ci. Although both of them were related to the Green Mountain Sect, they played different roles. The search results did not provide any clear information about their relationship. Therefore, there was no definite conclusion about the relationship between Liu Shisui and Liu Ci.
It could be some of the villagers who are jealous of Naruto's sudden growth under Shisui's training. They might try to undermine him or spread false rumors about him.
The main characters are clearly Itachi, Sakura and Shisui. Itachi is the one who is amused, Sakura is the one doing the pummeling and Shisui is on the receiving end of Sakura's attack.