In the fanfiction, it could be that Gai has been poisoned or influenced by a dark force. His behavior becomes erratic and he targets Tenten for some unfounded reason. Naruto, being the hero he is, jumps in front of Tenten to shield her. He might then try to find a way to cure Gai while also keeping Tenten safe. He could call on his friends like Sakura for medical help and use his own ninja skills to fend off Gai's attacks.
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.
Maybe Gai has some sort of misunderstanding about Tenten and is acting aggressively towards her, so Naruto steps in to protect.
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.
One possible plotline could be that Naruto and Tenten are on a mission together. Enemies attack and Naruto, being the selfless hero, puts himself in harm's way to protect Tenten. Maybe they are in a village that's being invaded, and Naruto uses his Rasengan to fend off multiple attackers while Tenten is injured or pinned down. In the end, Naruto sacrifices himself, leaving Tenten with a deep sense of loss and a newfound determination to carry on Naruto's will of protecting the village and its people.
One possible scenario could be Naruto being completely clueless about what to buy and Tenten having to guide him. Maybe they are shopping for ninja tools and Naruto is more interested in the flashy ones rather than the practical ones.
In the fanfiction, Naruto might be targeted by a powerful enemy who wants to steal his Nine - Tails chakra. Tenten, being a skilled ninja, steps in to protect him. She could set up all kinds of traps around their hiding place using her weaponry skills, and engage in combat with the enemy when they get too close, buying time for Naruto to regain his strength or for backup to arrive.
One way this could unfold is that Naruto and Tenten are on a mission together. They are suddenly attacked by a powerful and unexpected enemy. Naruto, being the selfless hero he is, sees the enemy about to strike a fatal blow on Tenten. He jumps in front of her without hesitation, taking the full brunt of the attack. His last moments could be him telling Tenten to keep fighting and protect the village.
Another storyline could be set in an alternate universe where Naruto has always been a swordsman. He and Tenten are part of a group of warriors. There's a tournament, and they decide to enter as a pair. They train together, and during this process, Naruto helps Tenten overcome some of her insecurities about her skills, while Tenten teaches Naruto some unique weapon - handling techniques.
One possible storyline could be that Godlike Naruto, with his immense power, takes Tenten on a series of challenging missions. He uses his unique abilities to protect her during battles against powerful foes. For example, when they face a group of rogue ninjas, Naruto's godlike speed and strength allow him to quickly dispatch the enemies while Tenten supports him with her weaponry skills.
Tenten would likely be deeply traumatized. Naruto was not only a comrade but also a symbol of hope and strength. His death in protecting her would make her feel guilty. She might start to question her own worthiness of being saved at the cost of Naruto's life.