"Naruto, for your birthday I've decided to gift you the title of Hokage for the day."
Naruto froze in shock as he heard the words the old man said to him. Disbelief shone on his face before it lit up in delight and he jumped in the air with a resounding whoop while Hiruzen chuckled at his antics.
"Now, I'll be off to have a nice day off today. Have fun, Naruto." Hiruzen placed the hat atop the ten year olds head before walking to the door, stopping right before he opened it. "Please try not to destroy the village in my absence, Naruto."
"You got it old man! I'll keep this place running smoothly or my name isn't Uzumaki Naruto!"
...
"Lord Hokage, are you sure this is a good idea?" Tenzo asked as he quietly followed the elderly Sarutobi. "This could go horribly wrong if he damages any political dealings."
"Don't worry, Tenzo, I've ensured that today there would be no politics, no high rated missions to hand out, nothing that could cause problems. I'll let Naruto have a fun day living out his dreams, while getting a day to myself to rest and be with my family."
"If you say so, Lord Hokage."
...
"Hey, secretary lady-"
"My name is Saki, Lord Hokage."
"Right, right. Anyways, Saki-nee-chan, I need you to do an important errand for me-ttebayo."
Saki saw the serious look on his (adorable)face and heard the tone he used, and she was briefly reminded of Lord Third when he had something needed to be done swiftly.
"Of course, Lord Hokage, how may I help?"
"I need you to go get me some ramen from Ichiraku, I haven't gotten my birthday special from them yet."
"...Of course, Lord Hokage."
...
"Lord Hokage, we've been sent word from Suna, they're once again asking to rework our alliance agreement." Shikaku announced as he entered the Hokage's office, looking through a folder. "I know you said it would be a bad look to turn away clients from Wind Country, but the Sand is get-"
Shikaku paused as looked at Uzumaki Naruto slurping a gigantic bowl of ramen while the Hokage hat sat comically big atop his head.
"...Naruto, where's Lord Third?"
"Hm? Oh, the old man is taking the day off and gave me the hat for the day, Shikamaru's dad. Anyways, what's this about the Sandy place?"
"...Suna." Shikaku shrugged his shoulders, too lazy to care if Hiruzen intended Naruto to deal with things of this caliber. "They're our allies, but in the past couple years the nobles of their country are coming to us for missions instead due to our better prices."
"Well that's dumb. Turn away those stupid old dudes missions and let the Sandy friends continue to be allies-ttebayo."
"Sure thing, Lord Hokage."
...
"...Lord Hokage, I'm not sure you're allowed to make today a new holiday named "Ramen Day"."
"I'm the Hokage-ttebayo."
"Lord Naruto, you can't keep using that as an excuse to do what you want!"
...
"Hey, mask guys!" Naruto called out before three ANBU appeared before him, making him jump slightly. "Shit! Don't do that-ttebayo!"
The ANBU in a cat mask giggled slightly while the others nudged her to shut up.
"Ahem, as I was about to say before you guys rudely interrupted me!" Naruto pouted at the three ANBU agents, "I want you guys to teach me some cool Ninjutsu!"
"...Like what, Lord Hokage?"
"I don't know, something cool and useful!" Naruto squinted his eyes shut, thinking to himself for a moment. "Oh! I know! Help me learn a Clone Jutsu! The stupid one they teach in school is dumb and I shouldn't need to learn it."
"Of course, Lord Hokage."
...
As Hiruzen walked back to the Hokage's office, he was pleased to see the village was not, in fact, destroyed in his absence.
"See, Tenzo? Nothing to worry about."
Entering the building, Hiruzen froze in shock and panic. There was about 50 Naruto's running around, carrying stacks of paper and chatting happily with other Shinobi and employee's in the building. His secretary, Saki, was calmly sipping a cup of tea.
"...Saki, what's happened since I left?"
"Hm? Oh, welcome back Lord Third. Lord Naruto has fixed various issues that arose, learned the Shadow Clone Jutsu, and somehow managed to instill a new holiday today withing hours of wanting it to happen. It was quite impressive."
"...What."
"Nothing to worry about indeed, Lord Third."
You shut up Tenzo.
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Happy Birthday to my boy Uzumaki Naruto, the little brat <3