Kamen Rider SIN and SHF were both characters in the Kamen Rider series. However, they had different backgrounds and storylines.
SIC was one of the characters in the Masked Rider series. It was a fictional creature created by Ishimori Shotaro who coexisted with humans and possessed superhuman strength and abilities. The main purpose of the SIC is to protect mankind from the threat of evil forces. It played an important role in the story and fought with other masked knights.
In contrast, SHF was another character in the Kamen Rider series. It was a fictional creature created by Shoutarou Ishimori that coexisted with humans but was more powerful than them. SHF's goal was to replace humans as the dominant existence of the world. It played an important role in the story and fought with other masked knights.
There are some key differences between the SICs and SHF in terms of storylines. The SICs 'story revolved around protecting humans while the SHF's story revolved around replacing humans. In addition, the battle between the SICs and the SHF was also an important difference between them. The SIN and the other Masked Riders fought together to protect humans while the SHF fought alone to replace humans as the dominant existence of the world.
Often, Gai is paired with Kakashi in Hurt Kakashi fanfiction. Gai, with his unwavering belief in friendship and his eternal rivalry with Kakashi, can be a great character to interact with a hurt Kakashi. He might try to pull Kakashi out of his slump through their friendly competition. Also, Rin is sometimes included. Since she has a significant past with Kakashi, her presence in the fanfiction can either be a source of comfort or more pain, depending on how the story is written.
In such fanfiction, the Kakashi OC often has unique physical features. For example, they might have distinct hair color or eye shape that sets them apart.
Kakashi might be initially surprised. But then, he would probably use it as a teaching moment for Naruto. He could say something like 'Naruto, stealing is not the way of a ninja.' And then give him a punishment like extra training.
Often, Naruto is paired with Kakashi in such fanfictions. Their bond from the original series can be explored in new ways in the context of Kakashi's reincarnation. For example, Naruto might be the one to discover Kakashi's reincarnated form and help him adjust.
Kakashi could use his Sharingan to analyze Obito's moves and find a weakness in his defenses. Since he has the Sharingan, he might be able to predict Obito's attacks and counter them effectively, eventually finding an opportunity to break free.
Kakashi's reaction would be complex. He is a man who has lost many people in his life. But Naruto was special. He would hold Naruto tightly, his hands trembling slightly. He might try to use some of his own chakra to keep Naruto alive a little longer, but deep down he knows it's futile. His face would show a mixture of pain, regret, and love. He would remember all the times he trained Naruto, all the lessons he taught him, and how Naruto had surpassed all expectations.
Well, one similarity could be their determination. In the fanfic, like in the original series, both Naruto and Kakashi are very determined. Naruto is always striving to become Hokage and Kakashi has his own goals and missions he's dedicated to. They also might share similar combat styles in the fanfic, perhaps Naruto starts to adopt some of Kakashi's strategic thinking during battles.
Kakashi would likely be very concerned. He would immediately assess Naruto's injuries. If they were serious, he would use his medical skills to start treating him right away. His first reaction would be to make sure Naruto was stable and out of immediate danger.
Kakashi might immediately offer a comforting presence. He could put his hand on Naruto's shoulder and just be there silently, letting Naruto know he's not alone.