So, yeah, it's been done a million times before, and Hetalia itself even references it, what with China often referring to England using the suffix 'ahen' (opium) instead of 'aru'.
Set sometime during the 1830s, before the outbreak of the First Opium War (1839-1842). England and America have a grand old time taking advantage of China and Japan, meant to be a teenager of around 16 or 17 in this, is quite frankly not best pleased by their behaviour.
Since this is set during the 1830s (before Japan opened trade with the West – aside from with the Dutch – following Matthew C. Perry's expedition to Japan in 1853), it can still be regarded as canon. The 'Modernisation of Japan' episodes with America are presumably set after the 1850s and the Anglo-Japanese Alliance episode where England hangs out with a kappa in a bath for like four hours is set in 1902.
Not so sure Japan would want to be friends with them after this, though.
"To what shall we drink?"
America, with a laugh in his voice as he raised his teacup, eyes almost too bright behind the glasses he had started wearing only recently.
England, admiring the colour of the tea as it settled in his own cup, looked up at him lazily through the smoke.
"To trade," he replied after appearing to give it a little thought. "To Asia. To China."
He gestured towards China on this; China, smoke coiling densely around his slender form as he lounged – barely able to hold himself up – across several pillows of rich red silk. His long black hair was wild and loose around his face and over his shoulders, his eyes were glazed and his pale fingers gripped the pipe possessively as he raised it to his mouth again, smiling languidly around it at his visitors.
"To China," he hummed, and then he laughed himself, tipping his head back slightly. "And to the British Empire and to the United States of America and to our friendship."
On his knees, arms wrapped around tiny little Hong Kong, Korea and Taiwan peeking out from behind him, Japan watched them in disgust. He was furious with China for having fallen for such a low trick, having previously believed him to have more sense; to say that he had come to greatly resent him was something of an understatement. And now what? Now Japan was left to look after China's charges while the so-called responsible elder traded tea for opium to feed the addiction England had convinced him that he needed.
And as for England – and as for America, who now showed up an awful lot as well... Japan didn't like either of them. In fact, he wanted nothing to do with them, or any of the other Western nations and their wicked influences, and he wished China wouldn't be so foolish. Neither England or America came here with goodwill, really – all they wanted was China's tea, and since they weren't terribly fond of parting with silver for it, they'd somehow gotten him to accept a drug as payment instead.
The air was thick with it, sweet and overbearing. Japan sat with the others far enough back to not be affected by it, only taste the stench of it, but the three of them that sat beyond the pinned-back curtain of thin purple silk were immersed in it. China was heavy in his habit by now and the smoke hung like a veil around the three of them, uniting them in their use of it (for one kind of gain or another).
America raised his cup to his mouth and drank deeply, sighing in satisfaction as he swallowed.
"Is it to your liking?" England asked, his tone mocking.
America just laughed again and took another mouthful; leaning over and kissing England, sharing it with him. England opened his mouth and swallowed it, threading his hands in America's gold hair and making him tilt his head more for a better angle.
China leaned forwards in mild interest, watching them.
"You like my tea, hm?" he sang as England broke the kiss and licked a stream of the stuff from America's chin.
"Your tea is wonderful, as usual." England turned his head away as America tried to kiss him again. "America, be polite. Tell China that you like his tea."
"I like your tea, China." America had his hands all over England as he said it. "It was a good trade."
"I am glad," China sighed.
England pried America's excited, wandering hands off, keeping him at bay long enough to take a sip of his own tea; he raised his green eyes towards Japan over the pretty porcelain as he did so.
Japan met his gaze and hated him. America was one thing (well, several: young and pushy and obnoxious), but England... Well, he was something else entirely – British Empire, as he was going by officially these days. Small and charming and well-dressed, every article of clothing just-so and in perfect order, from his cravat to his cuffs, he came across as very pleasant and amicable.
An act. A complete act. He was ruthless and greedy and manipulative and cruel. Japan saw it all in his eyes (too much like the jade China treasured) as their gaze met over the tea. The tea. That was all he wanted. That was all he wanted, that was why he kept coming here and—
Laughing. They were laughing at them – at China, at him, at Asia. Japan felt Korea twist the back of his kimono in his grasp. America had his head nuzzled against England's throat and he was laughing; and England tore his gaze away from Japan and rested his cheek on the crown of America's head and then he laughed too.
China clambered down from his perch amongst his nest of cushions and approached them, still holding his pipe. He reached them, fingers trailing idly through his own hair, as America kissed England again; he watched them for a long moment, as he had before, and then nudged at America's shoulder, trying to push him away, to pry them apart so that he could be included too.
America didn't take kindly to being given the suggestion that he should move over and shoved back, making China stumble. England pulled away from him immediately.
"America, don't behave like that towards our trading partner," he said sharply.
But he didn't sound dreadfully serious even so, and America didn't look as though he was about to apologise, blinking back at England somewhat dazedly as the empire pulled China in close and kissed him.
Japan stood abruptly, unable to watch any more of the horrible display. He grew to despise China more and more every day, but he couldn't take much more of this, couldn't stand to watch England smirk around the kiss as he drank China as wholly and delightedly as he drank his tea.
"Stop it!" he cried angrily, hitching up Hong Kong (who squirmed and fussed briefly in his arms). "China, this is—"
"Japan?" China pulled away from England, jet hair across his white forehead, and turned to regard Japan with some semblance of confusion. "I... was not aware that you were still here." He waved his hand dismissively at him. "You can leave. Go and put them to bed."
"China—" Japan started again frustratedly.
"Get out, Japan!" China shrieked at him, twisting himself out of England's grip enough to turn wildly upon the boy. "This is nothing to do with you!"
Out of the corner of his eye, Japan was certain that he saw England's gaze flicker interestedly towards Hong Kong the moment China was distracted; he did not process it fully, too stunned by China's sudden explosive outburst, but clutched Hong Kong (half-asleep, oblivious) closer almost out of reflex – or perhaps it was mere gut feeling, for he'd seen the ruin England was capable of. America, whom he had raised, and China, whom he had made fall, were both living, breathing testament to his greed and to his power (destructive as it was) even as they pawed all over him.
Japan drew himself up haughtily, regaining his composure.
"Very well," he said stiffly. "I shall leave, but only because this is hardly a spectacle that children should be an audience to. Come, Korea, Taiwan."
He turned on his heel and began to storm from the room, Korea and Taiwan scurrying after him, silent and scared.
"Nn... Japan!" American suddenly called, leaning over England's shoulder. "You need to be..." He paused, confused; having clearly inhaled far too much of China's secondary smoke. "You... you should trade with us too, open yourself up like China did..."
China smiled at America, dark eyes half-lidded, and then leaned to kiss him across England's lap, hair sliding like silk over his shoulders; Japan watched, too angry and disgusted to even speak, frozen in his place as England slithered his velvet-clad arms around them both and drew them covetously closer.
The empire looked upwards again lazily and met Japan's gaze a second time, all of his ruthless design and ambition present in those greedy green eyes.
His smile made Japan shudder.
Too bad you're one of the next on his list of countries to F-in-the-A, Kiku. XD
As for America being there... Well, the Opium Wars were fought between the British Empire and China because the British got all up in arms about China destroying some opium that apparently they had already traded tea for (making it theirs); China protested this, but Britain said that China had destroyed British property and declared war, yadda yadda...
However, the British weren't the only ones trading opium for tea with China. Contrary to popular belief, America (at this time) was also pretty obsessed with tea and, like Britain, wasn't overly fussed on shelling out Mexican Silver Dollars (the currency of trade at that time) for it – China would only take trade currency because neither America nor Britain had anything that they wanted to trade their tea for. Once the US saw that the British had come up with this ingenious idea to get the Chinese addicted to opium and then offer to trade the opium that they grew for practically-free in India for Chinese tea, the Americans thought 'Hey, we should get in on that!'.
So they did. With opium that they grew in Turkey. Voilà.
Fun Fact to Finish: We only gave Hong Kong back in 1997. Isn't that awful? DX