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.
One possible plot could be that Naruto was on a mission alone and got ambushed by a group of rogue ninjas. Kakashi, while out on his own patrol, stumbles upon the injured Naruto. He quickly takes Naruto to a safe place and uses his medical ninjutsu to stabilize him. Then, he might start to investigate who attacked Naruto and why, leading to a revenge - based sub - plot or uncovering a larger conspiracy against Konoha.
He'd probably be a mix of angry and sad. Angry at whoever or whatever caused Naruto to be in this state, and sad because he cares about Naruto so much. He might clench his fists tightly, trying to control his emotions while he focuses on helping Naruto. He'd also feel a sense of guilt, wondering if he could have prevented this from happening.
One possibility is that Kakashi would immediately use his medical ninjutsu to treat Naruto's wounds if he has the skills. Then he'd try to calm Naruto down by talking softly to him, asking what happened. He might vow to protect Naruto better in the future and start investigating the cause of Naruto's harm.
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.
One possible fanfiction could be about Kakashi getting injured during a mission. Maybe he's protecting his team and takes a powerful jutsu head - on. His students then have to figure out how to get him to safety and find a way to heal him. It could show their growth as they face this difficult situation.
Well, often in Hurt Kakashi fanfiction, there's the theme of his physical injuries and how he copes with them. Given his dangerous line of work as a ninja, he gets hurt a lot. Writers might explore how he deals with long - term or serious injuries that could potentially end his ninja career. Also, his relationships can be a source of pain. For instance, his complex relationship with Obito and how that affects his mental state when they are at odds.
Well, Kakashi is a complex character. When he discovers Naruto is abused in the fanfiction, he may first feel a deep sense of guilt for not noticing earlier. He'd then use his skills and influence in the village. He could start by reporting it to the proper authorities in Konoha, like the Hokage. And at the same time, he'd be there for Naruto, providing emotional support, talking to him, and helping him through the trauma. Kakashi has his own past traumas, so he'd understand what Naruto is going through on some level.
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.
You can try fanfiction websites like FanFiction.net or Archive of Our Own. Just search for 'Kakashi finds baby Naruto' on their search bars, and you'll likely find some relevant fanfictions.