He might be shocked at first. Naruto is used to seeing Kurenai as an ally, so being hurt by her would be unexpected. He could immediately ask her why she did it. If it was a serious injury, he might struggle to stay conscious while trying to understand the situation.
Naruto might be initially shocked and heartbroken. He is someone who values loyalty and friendship deeply, so being cheated on would be a huge blow to him.
One possible reason could be a misunderstanding. Maybe Naruto was misidentified as a threat in a tense situation. For example, if there was some sort of dark jutsu at play that clouded Kurenai's judgment and made Naruto seem like an enemy. Another reason might be that Kurenai was under some sort of mind - control. There are many villains in the Naruto universe who are capable of such things. If she was being controlled, she might unknowingly attack Naruto.
Sakura would probably be very angry at Kurenai. She's protective of Naruto and would demand an explanation. She might even try to heal Naruto right away if it was a physical injury.
There could be. Fanfiction is a vast world where all kinds of scenarios are explored. But it's not something that is part of the official Naruto storyline. You can try searching on popular fanfiction websites like FanFiction.net or Archive of Our Own. Just keep in mind that the content may be quite different from what you expect based on the original series, and it may also not be appropriate in some ways.
There could be many interpretations in such a fanfiction. Maybe it shows Naruto's vulnerability in relationships. It might be a way to explore his character deeper by putting him in a difficult emotional situation.
Naruto would probably be really confused at first. He respects Kurenai, so he'd be hesitant to fight back right away. He might try to talk to her and ask what's wrong.
Yuki would likely be very concerned. He has a soft spot for Tohru and would probably rush to her side, trying to find a way to help. He might even blame himself if he thinks he could have prevented it. Kyo, on the other hand, would initially be angry, but that's just his way of showing worry. He would be more hands - on in getting her the help she needs.
Simon might be in a bit of a panic. Since he's her friend and also not as used to the dangerous situations as the other Shadowhunters. He'd try to do whatever he can to help, like getting help from more experienced Shadowhunters or trying to comfort Clary while she's in pain.
Macgyver would probably be very worried. He'd quickly assess the situation and try to stop the bleeding if she was bleeding. He'd use his resourcefulness to make a makeshift stretcher or bandage.
His friends would most likely rally around him. Kiba might use his dog Akamaru to scout the area and make sure there are no other immediate threats. Hinata would be really worried and would try to use her Byakugan to see if there are any hidden enemies or if Naruto has any internal injuries. Choji would offer some of his food to Naruto to give him strength, as his clan's food can have special effects on a ninja's body.