Perhaps an enemy has used some kind of mind - control technique on Might Guy. This enemy wants to get to Tenten for some reason, like she has a special ability or knowledge that they want to eliminate or steal. So, they make Might Guy target Tenten. Or it could be that a new rule or mission has been given in the village that Might Guy misinterprets. For example, if there is a new security protocol and he thinks Tenten is violating it when she actually isn't, leading him to go after her.
Maybe there was a misunderstanding. Might Guy could have thought Tenten was involved in something bad, like stealing a valuable scroll from the village that he was trying to retrieve.
Naruto could use his shadow clone jutsu to create distractions. While Gai is busy dealing with the clones, Naruto can quickly get Tenten to a safe place.
It could be that Might Guy is under some sort of mind - control. So, without his normal self - control, he attacks Tenten, making it necessary for Naruto to save her.
Perhaps in the fanfiction, there's a misunderstanding. Guy Sensei thinks Tenten has stolen a valuable jutsu scroll or something important to him. Naruto, knowing Tenten is innocent, stands in front of her. He might try to reason with Guy Sensei first, using his charm and quick - thinking. If that doesn't work, he'll be ready to fight, using his Rasengan if necessary.
Maybe Naruto uses his shadow clone jutsu to distract Might Guy while he rushes in to grab Tenten and get her to safety.
Maybe Gai has some sort of misunderstanding about Tenten and is acting aggressively towards her, so Naruto steps in to protect.
Naruto could use his Uzumaki bloodline's chakra reserves. He might overwhelm Might Guy with a large number of shadow clones, confusing him and creating an opening to save Tenten.
Well, Naruto has his Nine - Tails chakra. He could potentially tap into that power to either overpower Might Guy or create some kind of shield around Tenten. He might also use his Rasengan, but in a non - lethal way to stop Might Guy's attacks long enough to protect Tenten. Also, Naruto is known for his quick thinking and adaptability in battle, so he could come up with a unique strategy on the spot depending on the situation.
Naruto might be really confused at first. He's used to people being friendly or having normal crushes, but a yandere is a whole different level. He'd probably try to talk to her and understand why she's acting so strangely.
Maybe Rock Lee could be an important character. He could come to the orphanage to help with the physical training of the orphans. He would be a great inspiration for them with his hard - working attitude. Also, Neji could be involved. He could use his Byakugan to keep an eye on the orphanage and make sure there are no threats approaching.
Their relationship could start with mutual respect. Naruto respects Tenten's dedication to her weapon - based ninjutsu, and Tenten respects Naruto's strength and determination. They might start training together more often, which would lead to them spending a lot of time together. This time together would allow them to open up to each other about their pasts, their fears, and their hopes for the future. As they grow closer, they would start to develop feelings for each other, and these feelings would eventually lead to their marriage.