The group decided not to inform Godzilla of their findings, fearing that he might choose to preemptively destroy Scotland now that his paternal instincts fully considered Harry his son. They also decided to only tell Harry that he was special, and to tell Godzilla that Harry might have powers other humans did not possess. He was still young and carefree, and there was no need to burden him with such weighty matters for as long as he remained on Monster Island, protected by both humans and kaiju alike.
Jet Jaguar, though loathe to abandon a case, put it on indefinite hold and resumed his patrols throughout the world. While Harry had become important to him, there were other foes to fight and more wrongs to right elsewhere. In particular, there were unconfirmed rumors of a kaiju sighting in Denmark of all places, so he set off after giving Harry his goodbyes.
So Harry Potter grew up without a care in the world until he reached age six. By that time he spoke English, Japanese, and a mix of grunts, growls, and even roars that let him "speak" directly to kaiju.
Now old enough to help with daily chores, he was sent out with a small group of Infant Islanders to gather water from one of Monster Island's larger lakes. The red water lake that Godzilla, Minilla, and (to a certain extent) Harry lived near was off limits that day, due to Godzilla teaching his elder son to use the atomic breath. And much to Harry's frustration, Godzilla still insisted that he was not ready to learn how to do that.
Such tasks usually passed without incident, but not today. Today Manda, serpentine god of the lost kingdom of Mu, woke from his slumber in the lake, disturbed by the sound of someone tripping on a rock and splashing in the water. The snake-like kaiju clambered out of the water on its vestigial limbs, hissing and growling at the intruders.
Harry, too immersed in the world of giant monsters to truly fear any of them, rushed forward and yelled, "STOP!"
Manda did. As the "second son" of the King of the Monsters, Harry was none too surprised, but he was thrown for a loop when Manda focused on him and spoke.
"A Speaker? It has been far too long since any conversed with me in the language of serpents. Tell me, young wizard, why have your companions disturbed me?"
The voice had only the slightest of sibilant qualities, but yet had a nearly unfathomable quality that suggested great age. Though Harry had communicated with kaiju before, none had ever spoken to him. The shock made Harry blurt the first things that came to his mind.
"We are sorry! It was an accident!… But what is a wizard?"
Though Harry believed he was speaking English (or possibly Japanese, sometimes he switched between the two without noticing), the Infant Islanders heard heard him hissing to the colossal snake and fled, this being far beyond any of the child's previous oddities.
"None of your elders have told you? Ah, you must be the adopted human hatchling Gojira and Mosura spoke of. In the tongues of men I am Manda, God and Guardian of the fallen kingdom of Mu, and eldest of the monsters. Behold!"
The serpent lifted full extent of his coils from the lake and used them to encircle Harry, providing the young wizard with an unobstructed view of all of his scales.
Confused and somewhat overwhelmed, the child once more spoke his mind.
"M-my name is Harry James Potter, and not to be rude, but why do you have so many scars?"
The snake god gave an inarticulate hiss and snapped, "Respect your elders, child! I was old when the first of Mosura's foremothers formed from the aether, and am not so desperate for conversation as to let such an insolent question stand!" Manda did not like to be reminded of his ill fated battle with the Atragon.
Frightened for the first time outside of the nightmares about green light, Harry backed away from the serpent's face and stuttered, "I am sorry, Manda! I am so small, and you are so large that I simply do not know how to act. I've talked to kaiju before, but none of them has ever really talked back, and I'm so confused and-and-"
To his shame, Harry began crying as he first felt the sting of isolation. As he'd said, kaiju never really spoke back, but it ran deeper than that. Sometimes he did things he didn't know how to explain, and while they never expressed fear the Infant Islanders sometimes looked at him strangely, and while the Shobijin never did that he could not truly play with them due to the size difference, which also applied the other way with kaiju. Such things normally did not bother him, but now alone and possibly in real danger of dying, he could see them with such clarity.
Manda's gaze seemed to soften. "Calm thyself child. It has been long since I spoke directly to a human, and longer still since I last spoke to a child. Now what was your question? What is a wizard?"
Through the haze of tears, Harry nodded.
"A wizard is a man blessed with powers far beyond those of most humans. You are young, untrained. You cannot control your power yet. No doubt when you feel strongly, strange things happen and others look at you oddly."
By now Harry had stopped crying, and was staring at the ancient deity with rapt attention. "Yes…" he murmured.
"That is what it is to be a wizard: to possess powers beyond those of ordinary men. One day you will be called to train, and you will have to choose what you want to do with your powers."
"But I can't make anything happen," Harry protested. "It always just does."
"And that is why you shall be trained. Do you see the fruit dangling from that tree?"
Harry looked towards where Manda was facing and saw it. A large, luscious Monster Island mango. A delicacy to humans and kaiju alike.
"You want it, don't you?" Manda inquired, with the tone of someone who already knows the answer.
"Yes…" Harry was barely resisting drooling. The one he could see was nearly the size of a watermelon.
"Someday you will be able to use your powers without emotion, but for now, focus on the mango. Think hard about how much you want it. Concentrate on how delicious it would be. And when you can barely stand it, envision it coming to you."
And Harry did so. Monster Island's mangoes were delicious, but took so long to grow and ripen that they were a rare treat for anyone. To keep one for himself would be incredibly selfish, but there was no one else around, everyone else had left him behind. He focused hard on how much he wanted it and how tasty it would be once he opened it up. It would be so sweet if only it would just come out of that tree.
He heard something snap.
Harry opened his eyes and saw the fruit floating towards him. Not falling, or it would have splattered against Manda's scales. Floating carefully until it was on the ground in front of him. Harry held it with a mix of awe and a strange exhaustion. Why would he be tired, he hadn't really done anything… right?
"Perhaps that was a bit too much for one so young, but consider that your first lesson."
A sudden familiar roar came from off to the side, and Harry turned to see Godzilla stomping towards them.
"Teaching," Manda replied to the titanic father, "I take it you thought he wasn't ready yet?"
Godzilla grunted and gave a low, menacing growl.
"Very well, but I would begin teaching him if I were you. The moth is not always right, as you yourself would know." And with that Manda slithered back into the lake.
The very next day, Harry had his first lesson in breathing fire.
Godzilla demonstrated first. The spikes on his back flared neon blue, and then azure radioactive plasma burst from his mouth. Then he gestured for Minilla to go.
Harry's elder brother only had stubs where his spikes would someday be, and they did not yet glow, but after taking a deep breath and seeming to prepare himself, Minilla spat a turquoise ring of smoke that eventually dissipated.
Now Godzilla gestured for Harry to go next. Details were difficult to express in the language of kaiju, but Harry's father managed to convey that he needed to draw from power deep within himself.
Harry concentrated, staring without seeing at the red water lake as he focused on feeling for some kind of power in himself. For a moment, he thought he felt something almost like a spark, and at that moment he took a deep breath and exhaled.
Out of his mouth came a blue ring of fire that faded away not far from his face.
Harry collapsed, feeling exhausted but pleased by that result, and Godzilla and Minilla both applauded him.
The kaiju sighting in Denmark isn't anything important, I just thought it would be funny to reference the relatively obscure Danish kaiju movie Reptilicus (1961). And I promise that the story will pick up the pace from here, I just needed these first few chapters to properly mesh the Godzilla and Harry Potter worlds.