AN: For pairing I'm going to go Samui, putting her at the same age as Naruto (already thought she was going into this story but apparently, she's several years older)
An Overheard Conversation
"…Let me get this straight." Sarutobi rubbed his temples, doing his best to restrain his growing Killing Intent, although given the glares from young Kurama and Kimmimaro the two morons were likely already suffering it. "You had both of your remaining students, Naruto's best friends, training with summons. You both were yourselves, training with summons. All while sending Naruto, a young man who you know has abandonment issues and a desperation to fit in and be included, was sent to train in something else being the only person without a summon contract…but did not once think this was a possibility?!"
"It's…it's obvious on hindsight." Kisame winced, Hiruzen's restraint on his killing intent finally slipping as Itachi and Kisame paled further.
"We already had the summons from our three contracts return to their bosses to have them talk to their allies in the summon realms." Itachi stated quickly, "And I contacted Gai, Kakashi, and the Inuzaka clan to have them check with their own summons. I'd have asked Anko, but I didn't want to risk the information getting back to Orochimaru."
"At least you thought that far ahead." Hiruzen felt his growing headache forming "There's nothing we can really do at this point but wait. I'll be making sure the Academy will be doing a special lesson about why doing what Naruto did is imbecilic in the extreme. You two however will be D ranks, without pay mind you, for the next month." It spoke volumes to either their awareness to how bad they'd messed up or how terrified they were of him that neither lobbied even the smallest hint of protest.
"Yes Hokage-Sama." Itachi and Kisame nodded in acknowledgement.
"By the way, there's one more person I called in to discuss this issue with you." Sarutobi had to hide his sadistic smirk, "Someone who is quite fond of young Naruto." With a wave to one of his Anbu, they led the Ichiraku girl in as the civilian started tearing Kisame a new one, the S ranked Shinobi cowering before the fury of the untrained girl while Itachi kept silent to avoid earning any ire as well. It was quite amusing seeing the shark like man so obviously smitten without realizing it. He'd have been tempted to give the boy a wake-up call but after this that wasn't likely.
"Oof!" Naruto let out a grunt as he landed, the summon dropping him into the realm of his new partners, "Now where am I?" he looked around at the dark misty forest "…And why is everything I touch sticky?" pulling his hand from the ground he saw thick white strands coming along with it. "Hello?
Naruto shouted out, the question echoing through the trees "Is anyone out there?" A rustling sound came from deeper in the trees, something having apparently heard his shout and was coming to investigate.
"Hi there!" a new voice spoke up from a tree branch as Naruto turned, trying to find the source only to see a very small spider waving a little leg at him "I'm Lucas!"
"I'm Naruto!" Naruto grinned, waving at the little spider.
"You're not a spider, how are you here?" Lucas tilted his little head confused as he looked at Naruto.
"I did a reverse summoning." Naruto frowned "My friends all have summon partners but me. But at school they told me that if I do the jutsu without having signed a contract I'll get brought to the Summon partners that work with me best!"
"That's so cool!" Lucas gasped, putting his two front legs to his face while he looked at Naruto wide-eyed "That…that means you're like a destiny buddy!"
"Destiny buddy? I like it!" Naruto held out a finger for Lucas to 'high-five', the little spider doing so with a happy giggle "So Lucas, where's everyone else?"
"They're dat way!" Lucas pointed towards the direction the rustling sound, which Naruto had forgotten about, was coming from "But I think they're getting closer." As if waiting for a cue to enter, another spider exited the mist, this one the size of a small house as compared to Lucas who would easily fit in the palm of Naruto's hand.
"Hi Auntie Gwen!" Lucas waved "This is Naruto!"
"Lucas, what have we told you about talking to strangers?" The new bigger spider, Gwen apparently, scolded Naruto's tiny new buddy.
"To not to. But he's not a stranger, we know each other's names. And he's a destiny buddy!" Lucas protested.
"…A what?" Gwen turned to inspect Naruto in confusion only to double take when she saw his expression.
"So cool!" Naruto gushed at meeting another new summon "Are all the spiders here as big as you? This is the best contract ever!" he held out his hand for Lucas to high five again, the little spider doing so before zooming on top of Naruto's head like a hat.
"…Contract?" Gwen leaned down to inspect him "You reverse summoned yourself? And it brought you…here?"
"Why do you sound surprised?" Naruto tilted his head "You look awesome."
"I'm a spider." Gwen deadpanned.
"So?" Naruto and Lucas asked in tandem, both confused as could be while Gwen sighed.
"Whatever. Still, you don't have a summon contract yet. The boss needs to decide you're worthy for that to happen." Gwen informed him as she picked him up between her fangs.
"Don't worry, Momma's real nice!" Lucas promised, happily remaining as a hat while Naruto was carried rapidly through the misty woods, the spider webs in the trees growing thicker and more numerous the further they went in.
"Gwendolyn." A raspy hissing voice demanded from the shadows when they finally made it into a clearing "What was the disturbance?"
"A human Lady Arachne." Gwendolyn answered, dropping Naruto onto some webs "This boy did the summoning Jutsu without a contract and was brought here." As she spoke, Naruto did his best to see how big this 'Arachne' was. She was definitely bigger than the boss summon for the Monkeys and Ravens, although he hadn't seen a boss for the Sharks yet, so he wasn't sure if they were small or the norm.
"Hi momma!" Lucas waved to the massive spider queen "This is Naruto, he's really nice!"
"That's good dear." Arachne leaned down to get closer to Naruto and Lucas "Boy, I smell no fear on you."
"Why would I be scared?" Naruto tilted his head in confusion "The jutsu taking me here meant you all were the best partners for me. Plus, you're awesome!"
"Hmph, most humans seem rather scared upon seeing even a regular spider, let alone one of our grandeur." Arachne scoffed.
"Most humans are dumb." Naruto shrugged "A lot of people in my village treat me the same way."
"Is that so?" Arachne continued to inspect him as other spiders scuttled down "Who are you child?"
"Naruto Uzumaki, future Hokage!" Naruto jerked a thumb at his chest with a grin.
"I have heard of your clan." Arachne nodded "But what of you? I would need to learn of you as a person so you must pass my test. Show you are worthy to be a member of the Spider clan. Show me what value you could bring to my family."
"Um… I can do these." Naruto focused and made his chakra chain, "I might be able to make something like a web out of these with more training." He considered "I can do Dust release…Ooooooh! I'm really good at pranks!" he chuckled "At one point I painted the Hokage Monument carved into a mountain and nobody saw me doing it till I was done and shouted at them to look."
"I detect no lies Lady Arachne." Another spider, this one not nearly as big as the boss but with milky white eyes spoke up, staring at Naruto with the blank orbs "He seems to be honest."
"That's not all. I sense something within him." An old sounding spider with milky white hairs slowly approached, the other Spiders all seeming deferential to the ancient one "Something powerful…something ancient. This boy has potential Arachne, I saw we let him summon us for now, see how he does."
"Very well Anansi." Arachne nodded to the ancient one "My son and the Clan Elder have spoken up in your favor child, so you may form a contract with us. Know this though, betray our alliance and this contract shall be ended, as will your life if we get our fangs into you!"
"I would never!" Naruto protested hotly, shooting to his feet even as Lucas held on tight "I never go back on my word, that's my Ninja Way!"
"Hmph, we shall see." Arachne shot a web up into the trees, pulling it back as a scroll came along with it "You must sign in blood, and then I shall mark you with our clan's crest."
"Sweet!" Naruto grinned, using a Kunai to prick open his finger to sign the scroll which he saw had almost no names on it, and definitely none done recently. Contract sealed he looked up at Echidna who approached, dropping some venom onto his palm as the liquid burned his skin, mingling with his chakra to form a spider like emblem on his arm.
"The contract is sealed." Arachne declared, summon us as needed, but know that we shall be watching." With that, he felt a tug in his gut before he was surrounded in a cloud of smoke, reappearing in the training ground with a poof.
AN: So yeah, I went with Spiders as I was thinking they really would be a good fit for Naruto. Clever, sneaky, good with traps and tricks. Plus, much like Naruto, people tend to see them and instantly feel disgust or fear so there's a kindred relationship there.