It could be Orochimaru. He might be interested in Ino's unique abilities, like her mind - control jutsu, for his own evil experiments. So he kidnaps her, and Naruto has to fight against Orochimaru's snake - like techniques to save Ino.
The Akatsuki could also be the villain in this fanfiction. They might think that Ino has some valuable information about the Hidden Leaf Village. They capture her, and Naruto has to take on members of the Akatsuki, which is no easy feat. He'd have to use all of his training and strength to defeat them and rescue Ino.
One possible plot could be that Ino is captured by a group of rogue ninjas. Naruto, being the hero he is, senses her distress. He embarks on a journey to find her. Along the way, he overcomes various obstacles and battles. Once he reaches Ino, he uses his powerful jutsu to defeat the rogues and save her. Then they return to the village together, with Ino being very grateful to Naruto.
It could be a rogue ninja from Orochimaru's former experiments. This ninja might hold a grudge against Anko for betraying Orochimaru and decides to target her. Naruto would then have to face this powerful and vengeful enemy to save Anko.
Perhaps an evil organization that wants to capture Ino for her unique mind - related abilities. They believe they can use her powers for their own malicious purposes. Naruto and the rest of the team then have to protect Ino and take on this organization. The leader of this group could be the main villain, with his own set of powerful and dark jutsu.
A rogue ninja from a neighboring village could be the villain. This ninja might have a vendetta against Ino's family and uses Naruto as a tool to get to her. He hypnotizes Naruto because he knows Naruto is strong and his actions while hypnotized would create a lot of trouble for Ino and Konoha.
A rogue ninja from another village who is jealous of Ino's talents and the reputation of her village could be the villain. This ninja might think that by kidnapping Ino, they can bring down the morale of her village and prove their own superiority.
A powerful and mysterious organization could be the main villain. They have been secretly manipulating events in the ninja world for years, and now they plan to use a powerful weapon to destroy all the hidden villages and take over the world. Naruto has to expose and stop them.
In a 'Naruto Saves Ino' fanfiction, a possible plot point is that Ino is about to be sacrificed in a dark ritual by a cult - like group of ninjas. Naruto discovers this and battles his way through the group's defenses. He might also have to use some of his sage mode abilities to overcome the various traps and barriers set up by the cult. Another interesting plot could be that Ino is poisoned, and Naruto has to find an antidote in a limited amount of time. He could enlist the help of Sakura or other medical - nin in the village, but ultimately it's his determination and quick thinking that saves Ino.
Well, perhaps Naruto has been observing Ino for a while and when he finally sees the school bullies picking on her, he steps in without hesitation. He might use his Uzumaki charm to first try and talk the bullies down. But if that doesn't work, he'd be ready to fight. His Rasengan might not be necessary but his basic ninja skills would be enough to send those bullies running. And this event could be the start of a closer friendship between Naruto and Ino.
Maybe an evil wizard - like character from a far - off land. He hears about the pet in the Naruto universe and decides to capture it to use in his dark magic experiments. His arrival in the village causes chaos, and Naruto, Ino and the pet have to stop him from achieving his evil goals.
Well, in the fanfiction, Naruto could save Ino from Sasuke by appealing to Sasuke's former friendship. Naruto might talk to Sasuke, reminding him of their days in Team 7 and how Ino is also their comrade, which makes Sasuke change his mind and let Ino go.