-Chapter 3, Subchapter 1: The First Day of School, Class 1A-

At the beginning of school, Goku was dressed in his UA uniform. He wore his tie a bit too loose and his outfit was tight on his adult-like body, and he elected to try to hide his tail by using it as an impromptu belt, but he soon meets up with Midoriya and Uraraka.

"Hey, Goku-kun!" Uraraka said with a warm smile. "Thanks again for your help at the Practical Exam! If it weren't for you and Deku-kun, I would have been in serious trouble!"
"Oh, so you're that Midoriya All Might was talking about!" Goku gleamed with a bright smile at Midoriya's direction. "Man, that punch was intense! I don't think even I could have done that!"
"D-Don't discourage yourself, Son Goku!" He replied, still a bit stuttery, but a fair bit more confident than last time. "You were moving like a blur and taking out those robots like they were made out of paper!" Goku chuckled as he said that, scratching the back of his head.
"Also, that rescue was nothing, Uraraka! It was just how my parents raised me, to help others if they're in trouble!" he said, with a smile on his face, she smiles brightly and nods in appreciation.
"Anyways, we should go and find Room 1-A before we're late," Midoriya reminded, as the two followed him.

It took a while going through the labyrinth of hallways that made up that glass H building, but they soon found themselves at the giant door to Class 1A. Upon opening it, the students looked at Midoriya and Goku, the student who rescued their test mate and the student whose attack was unrelenting. There was positive murmurs as the three found their seats.

"There's that orange gi kid that thrashed those robots like they were toothpicks!" a pink skinned girl said, with a wide grin hiding the fact she had black eyes. "And that manly green-haired dude that saved that girl alongside him!" a red-haired kid added on. "S-Such cool guys!" A small, purple-haired kid spoke up. "Please forgive me for doubting your abilities during the Exam! I hadn't realized the second part until those letters were sent out and for that, I must apologize!" the tall, glasses wearing guy said towards Midoriya's direction. "I saw your performances, they were... admirable." a white and red haired kid commented, not raising from his seat. Bakugou only shot daggers at Goku and Midoriya as they take their seat.
"Man, that explosive kid's a grump!" Goku bemoans. The gall of this bumpkin... dismissing him as just a "grump" because he only had 56 points while he had 77?!
"I'll kill you, you worthless piece of monkey trash!" he yells, as he tries to get closer to Goku, his eyes narrowing on the blonde kid, as if to challenge him.
"Kacchan, no!" Midoriya said, trying to move between the two.

But then the three felt a red glare fall upon them as the two boys returned to their seats. A tall, perpetually tired man comes in, and the class hushes. He wears all black and has a truly large scarf resting on his shoulders, partially obscuring his mouth, alongside a sleeping bag in his arm. For some reason, Goku's back tingled as he looked at the glare.
"That's enough rowdiness for today, class. Such a thing is irrational and will only serve to hurt you. I am Shota Aizawa, and I'll be your home room teacher. For orientation, we will do a Quirk test." He said. The class murmured again, this time wondering about the test.
"Wasn't the Entrance Exam a test?" "Yeah, that should be all that there is." "Maybe it's a more detailed test?" "Should we attend orientation, Aizawa-sensei?"
"Silence," he commanded, his eyes flashing red again as his students shuts up. "Hero work isn't all fun and games, as some of you may have read online, and the Principal had allowed me and my coworkers to teach in any way we want. As well, orientation as your middle schools have done them is a waste of time if any of you aren't worthy. This test will make sure you're proven to stay in my class. It's one thing to be able to defeat machines, it's another to make sure you're well-rounded as a Hero-in-training," he continued. "Now, everyone get your gym clothes and meet me at the P.E. Grounds in ten minutes. You are to use your Quirks to help me determine if you're indeed worthy to stay in my class." The students prepare their bags, heading downstairs to go and change up for this surprise test.

-The Quirk Apprehension Test: Enter Mr. Aizawa-

"Good, you're all here on-time. Compared to the last class, you're already doing better. The first challenge is the fifty-meter dash. I will time your speed. Most of you, if you're in 1A, should be able to pass without problem. Unlike in middle school, where you all are expected to do it normally, you will use your Quirks in conjunction, so that I may have a baseline for your potential. Asides from Son Goku, who was home schooled." Aizawa remarked. "Speaking of such, before we get started, Son Goku, as you have gotten first in the Entrance Exam, you're the first to pitch the ball. Throw it as far as you can so that I may gauge your Quirk potential," Aizawa instructs.

Goku winds up a pitch, his tail relaxing as it finally extends out as he concentrates, and throws the ball right as Aizawa's irises flash a menacing red. Despite the glare, Goku's pitch landed 1.4km away, subtly shocking the teacher as he holds the result up to the rest of the class. "One point four kilometers," he read out.
"That's his pitching strength?!" "I expected no less than someone who can punch robots in the face with no trouble!" "Son Goku? Like the son of the Rice Hero, Mochi-Mochi? How is he so strong?!" "This'll be so fun!"
"Heh, is it fun? I had neglected to mention this before Son Goku's pitch. The person who lands in last place will be expelled. Do not disappoint me." Aizawa warned as he glared yet again, everyone stops talking in silence, Midoriya turning deathly pale. "Now, let's start the test."

And so, the Quirk Apprehension Test begins. Goku, by nature of his training, is doing exceptionally well.
On the 50 Meter Dash, Goku blitz'd through with a blazing 3.12 seconds, beating out a blonde kid with a tail, whose speed was 6.47 seconds. On the Grip Strength, he outright broke the device recording the grip strength, last recording 900.1 kg, his teacher glaring at his student and the student giggling a little sheepishly. Less impressively, as many of his student already did, the black-haired kid landed well outside the sandbox with a powerful leap. Weirdly enough, the Side-Jump was one of Goku's weak points in his otherwise monsterous performance.
Aizawa kept on eyeballing his records, shocked because that kid, Son Goku, doesn't even seem to use his Quirk, and yet he's going beyond superhuman records with at least one of the records, and is still well within superhuman standards with the other one. He also notes that Izuku Midoriya is on the opposite end: not using his Quirk, but is also virtually dead last in everything, noticing a panic within the boy, something he'll need to shed off if he'll be successful in his class. In the meanwhile, Goku first sees some of the kid's Quirks in action in detail. Aoyama's Naval Beam, Iida's Engines, Bakugou's Explosions, Ashido's Acid, Mineta's Pop-Off, and was in awe on how they used their Quirks to be as agile as he is.

Finally, in comes the Pitch, right in the middle of the test. It went in sequential order, Bakugou pitching second. A wind up and an explosion, he cursed himself as he saw that his baseball was only 705.2 meters out. Soon after, Midoriya goes up to pitch the ball. At first, he tries to use his entire arm, crackling with red cracks, only for Aizawa to stop him with his Erase Quirk.
"Izuku Midoriya, your Quirk is powerful, but it's useless if you need to be rescued because you break your body after a single use. I will give you a last chance, but if you can't move your arm, you'll be expelled immediately."
The students looked anxiously at Midoriya, while Goku looked at him with hope in his eyes. All Might spied from afar, also turning a similar pale. The next pitch by the green-haired kid went off much better, as he used his Quirk in his fingertip to reach a Hero-like record of 705.3 meters, pleasantly surprising the Eraser Hero.
"That's a Hero record!" Uraraka said with excitement. Goku was beaming with joy, and much of the student body was happy to see that Midoriya had been able to control his Quirk to limit the damage on himself. Aside from Bakugou attempting an attack on him and getting wrapped up in his teacher's Capture Cloth, the rest of the pitches come to an end and the scattered remaining exercises came to an end, with Goku patting Midoriya on his back, alongside Uraraka and Tenya assuring him he did well. The final three tests, with little surprise, Goku dominated. Pull-ups, Sit-ups, and plenty of juice made sure of that one.

"That's the test. I'll show you the test results soon. However, before I do so, I had neglected to state that the expulsion threat was a lie, a logical ruse to make sure you gave it your all." Aizawa said, a humongous, shit-eating grin emitting from this perpetually tired frame.
Everyone aside from a black haired, tall girl looked flabbergasted and relieved at the deception.
"It should have been obvious from the start," the tall girl said, a bit annoyed. "However, I can't argue with the results of spouting such a falsehood."
He showcases the results to the body. Midoriya was dead last, and Goku scored first due to his sheer strength and agility making him well-rounded. Momo Yaoyorozu, with a second place score, looked at Goku with some intrigue. Actually, that kid... he looks familiar somehow. However, before she thought any deeper, she looked at Aizawa as he started to speak again.
"However, I will not accept anybody holding back. Especially you two, Shoto Todoroki and Son Goku," Aizawa glared at the red and white-haired kid. He simply looked elsewhere, not concerned about his opinions. Goku felt himself scratching the back of his head and giggling, while the rest of the class looked shocked. That's Goku holding back?! He was a monster and a half with his performance as it was!

"The rest of you are free to go, your curriculum are on the desk, except for Son Goku. I need to talk with you, out here about something I picked up on." Goku is confused, as he waves goodbye to Midoriya and Uraraka.
"What's the problem, Aizawa-sensei?" Goku asks.
"There's something about you, Son Goku. You were able to achieve Hero records with just your strength alone. You were able to rival Tenya Iida's 3 seconds and decimated all but Uraraka and Yaoyorozu with your pitch, and yet it felt like you were still holding back. Keep this in mind when we conduct our exercises throughout the year. You may go, but I will keep my eye on you. Hold back on me, and you will be expelled, problem child," Aizawa said.
"Okay, Aizawa-sensei! I will not let you down" Goku eagerly runs off to rejoin his class, but he was shocked when he was stopped by All Might himself when he entered the school.
"I am honored to finally meet you in the flesh, Young Goku. I had seen how you did in Aizawa-sensei's impromptu orientation, and I see that my predictions on your potential were not unfounded! I hope to see you soon in class," The No. 1 Hero belted out a laugh. Goku was starstruck, but he soon was on his way back to 1-A as the giant Hero went outside, probably to speak to Mr. Aizawa, his grin lessening since that threat wasn't a lie, at least that's what the 1st Years of last year said.

The students of 1A were talking, messing around and being teenagers when Goku came in. Silence took hold, as they looked at him. Many were in shock and awe with how he's able to keep up with them by his pure physical might, while Bakugou was staring daggers at him, and Momo and Shoto looked at him with a stoic expression on their faces, though with the former having a betrayed interest in her classmate.
"His speed is absolutely crazy!" "Even that weird glare thing Aizawa did didn't scare Goku! He must be fearless!" "Of course, it's the same guy that scored 120 points at the Entrance Exam!"
He walks back and grabs his cirriculum, and soon everyone walks out, the bell having rung. Goku, Uraraka, and Tenya see Midoriya heading towards them, the former two waving happily while the latter has a finger wrapped up.

"Hey Goku, Uraraka, Tenya!" Midoriya said, pretty happy, but having his index finger tied to his middle finger, along with a small lipstick mark where Recovery Girl kissed him
"Deku-kun!" Uraraka blurted out, a bit worried about Midoriya's broken finger. "Is your finger okay?"
"How is your finger, Midoriya-kun?" Tenya also asked.
"Oh, it'll be fine, but I need to get better at managing my Quirk..." The green-haired teen's expression soured a little upon saying those words, feeling disappointed.
"Hmm? Oh yeah, now that you mentioned it, you broke your arm and your legs because you couldn't use your Quirk effectively in the Entrance Exam!" Goku chimed in, unashamedly as he didn't think in the moment on how his classmate would respond.
"Y-yeah..." Midoriya said in a hushed voice, retreating himself inside his uniform.
"It reminds me when I trained as a kid! My martial arts teachers often talked about managing my power so that I could fight on par with the other kids and some of the adults in the class! Otherwise, it'll be as easy as smashing an egg!" Goku chimed in.
"Fight on par with adults, otherwise they'll be smashed like eggs?!" Uraraka and Midoriya said in shock, Tenya's face also painted with shock.
Midoriya was thinking about power control, but how...? It seemed binary how his power worked, either he can go full tilt or not at all, like a light switch! What if... he treated it more like a light slider? If he trains a little, he can find his safe limits! He internalizes Goku's comment about power management, as he hopes he can find his own limits tonight, or else he'll be significantly disadvantaged against everyone.
"Ah, that's why you were able to take apart these robots during the Entrance Exam with ease, Goku-kun!" Tenya exclaimed, having shaken off the shock.
"Yep! But seriously, there were so many cool abilities I saw! Like your floaty touch, Uraraka! Your fast legs, Tenya! Bakugou's Explosions! Aoyama's lasers! And that Todoroki guy's ice was like no other!" Goku gushed over.
"I-It makes sense, Todoroki was recommended by Endeavor, the No. 2 Hero," Midoriya mused, before he started to mutter himself on all the Quirks he saw, "...so many notes to take, so little time...!"
"Oh! I can't wait until we get to fight, it'll be so much fun!" Goku said, his child-like giddy getting him excited to think about the fights with his classmates. They aren't just low hanging Villains with lame Quirks, they were people with powerful Quirks! There's something within him that flared, that thing craving more fights, and a lot of his classmates have that spirit!
"See ya tomorrow, Tenya-san! Goku-kun! Deku-kun!" Uraraka said as she left.
"Goodbye for now, Uraraka-kun, Goku-kun, and Midoriya-kun!" Tenya bowed before he left. "I'll see you tomorrow, Uraraka-san and Iida-san! And I'll consider what you said, Goku-san!" Midoriya chimed, as he left.
"See ya later!" Goku bluntly yelled to his friends, before he went home. Despite the light scoldings of Mr. Aizawa, his first day went fantastic, and he had such a fantastical story to tell to his parents, happy that Goku had taken well to the school life.

AN: For a lot of this part, a good chunk of the story would likely stay the same, just replacing Sato with Goku. However, Sato is still in UA, he's just in Class 1-B. Unfortunately, Mineta has more importance tied to him in the early game than Sugarman, so it was easy enough to replace the poor stronk sugarlover. Not to worry, his delicious ass cakes will still be here.