I'm not sure if there is such a specific fanfiction. Fanfiction can cover a wide range of ideas, but this particular concept might be quite rare or even against the general canon and ethical boundaries in some ways.
In literature, stories of girls and boys getting a spanking were more prevalent in the past. They were often used to illustrate moral lessons. For instance, in stories set in Victorian times, spanking was seen as a normal form of punishment for naughty children. This was also a way for the authors to show the strict social and family structures of that era. As time has passed and ideas about child - rearing have evolved, such stories have become less frequent in contemporary literature.
In 'A Tale of Two Cities', the young and innocent Lucie Manette faces great hardships during the French Revolution. Her world is nearly 'destroyed' as her loved ones are in danger, and she has to endure the chaos and violence around her.
I'm not sure of a specific one, but it could be that in a fanfiction, the mouths on his hands are used to communicate with ancient spirits. Naruto might be the only one who can do this because of some special connection, and it helps him gain new powers and knowledge to protect the village.
There's 'The Sand and the Leaf's Union'. This fanfic focuses on the political implications of their marriage. It shows how the two ninja villages, Suna and Konoha, start to collaborate more closely as a result of Gaara and Naruto's relationship. The story also has some really sweet moments between the two characters, like when they go on secret dates in the forest between the two villages.
A new and powerful rogue ninja could be responsible. This ninja might have a vendetta against Konoha and see Naruto as a symbol of the village, so they target him and use their strong and devious techniques to injure him badly.
Well, one possible plot could be that Naruto somehow stumbles upon a portal or a hidden area in the Naruto world where Xenomorphs exist. Maybe Orochimaru was doing some forbidden experiments and accidentally opened a gateway to their dimension. Naruto, being the curious and brave ninja he is, decides to explore. He then has to use his ninja skills like his shadow clones and rasengan to fend off the Xenomorphs. He might also try to find a way to close the gateway to prevent the Xenomorphs from spreading across the ninja world.
In fanfiction, when Naruto gets injured by Pain, it could also trigger some new powers or abilities within Naruto. Maybe the injury acts as a catalyst for him to tap into a deeper level of the Nine - Tails' chakra. His injury might also make the other villages more aware of the threat that Pain poses. They could decide to form alliances with Konoha in order to deal with the Akatsuki as a whole. This would change the political landscape in the Naruto world.
One possible plot could be that Naruto discovers a strange power that somehow gives him the Senbonzakura ability. He then has to learn how to control it while still using his own ninja skills. Maybe he uses it to fight a new, powerful enemy that his normal jutsu can't defeat.