Well, I'm not sure of the exact name, but there's a 'naruto finds an army' fanfic where Naruto finds an army of ancient warriors. These warriors were sealed away long ago and Naruto accidentally releases them. At first, they are hostile, but Naruto manages to convince them to help him fight against a common enemy. The fanfic is really interesting as it combines elements of Naruto's world with ancient legends.
One main theme is leadership. Naruto has to step up and lead the newly - found army. He has to make decisions and inspire the members. Another theme is unity. The army, which may consist of different types of people or beings, has to come together and work as one. For example, if there are members from different villages in the army, they need to put aside their old rivalries.
Well, he might be initially confused. Naruto comes from a world with ninjas, not a modern army base. He could think it's some new kind of enemy stronghold. Maybe he'd try to infiltrate it in his typical ninja way, using stealth and jutsus.
In a fanfic where Naruto finds an army base, he might initially be on high alert. He could use his ninja skills to scout the area stealthily. Maybe he would try to figure out if the army base is a threat to his village. If the people in the base seem hostile, he would likely be ready to defend himself using his jutsus like the Rasengan.
Another possibility is that he discovers a hidden room with a secret about the history of the ninja world. This could be related to a long - lost clan or an old war that has been forgotten. Naruto would then have to decide what to do with this new information, whether to share it with his friends or keep it a secret for the time being.
I'm not sure of a specific 'naruto finds the sekirei ship fanfic' off the top of my head. You could try searching on fanfic websites like FanFiction.net or Archive of Our Own. They have a large collection of fanfictions and you might be able to find one with that specific plot there.
Sasuke would be more aloof about it. He might not show much interest on the surface, but secretly he'd be observing Naruto's every move. If there was something in the base that could help him in his quest for power, he'd definitely be interested.
One possible plot could be that Naruto is on a mission in a mysterious land and stumbles upon the Golden Army by accident. Maybe he initially mistakes them for some kind of powerful jutsu - created constructs. As he tries to figure out what they are, he discovers their unique powers and abilities. He then has to decide whether to use them for the good of his village or leave them be as they might be a dangerous unknown force.
Some of the soldiers in the base might be scared. Naruto's appearance, with his orange jumpsuit and strange ninja tools, would be really out of the ordinary for them. They might think he's an alien or some sort of super - powered threat.
The main antagonists could be those who want to use the Golden Army for evil purposes. Maybe some rogue ninjas who see the power of the Golden Army and plan to use it to take over the ninja world. They might try to steal the Golden Army from Naruto once they find out he has discovered it.
One popular 'naruto finds a shield' fanfiction is 'The Shield of the Hidden Leaf'. In this fic, Naruto discovers an ancient shield with special powers during one of his missions. The shield has the ability to deflect even the most powerful jutsu. It becomes an important part of his arsenal as he faces tougher and tougher opponents.