It took Danny a couple of weeks to gather all the necessary ingredients for the potion he was planning, especially because he could only gather them in the few times to himself he could scrounge up between shoveling manure and all the other menial tasks he now had to perform (and bedtime with Brian, of course). Most of it was various herbs that he knew from experience where to find around the farm, along with other things like songbird feathers, goat's milk, morning dew, and Brian's hair and sweat (very easy to collect, since his hair was all over their bed, and he was more than happy to let Danny rub him down with a rag after a long day of hard work). Through it all Brian followed Danny like a giant puppy. Danny hadn't actually told Brian why he was gathering all these things, unsure of how he might react to being told of his plan, but the big dumb oaf was hardly curious, just content to follow his love around.
Finally, the time for Danny to put his plan into action arrived. His father and brothers left on the cart along with several of their farmhands, to take their wheat, fruit, eggs, chickens, and pigs to market. The farmhands that remained were under strict instructions to keep Danny from entering the house, but these were abandoned for the sake of drinking and dicing as soon as night fell. Even so, Danny decided to be cautious, leaving a distraught Brian behind ("I have to go do important things, but don't worry, I'll be back soon") and slipping in through one of the back entrances he was familiar with (he had spent his entire life in the house until a few weeks before, after all) using a surreptitiously snatched key. Inside the house, he found himself surrounded by all the trappings of prosperity that he had been forced to leave behind, and took only a brief moment to savor those memories of his old life before moving on to his room where, fortunately, his alchemy set lay untouched (as if any of the cretins in his family would be able to do anything with it). It took a lot of work and he had to refer to his also-untouched books several times, but by dawn Danny had a potion in a vial that he was sure would break the spell over Brian and reveal the sensitive, intelligent elf that lay hidden beneath the dull-witted farmhand. He returned to where Brian had fallen asleep outside, woke him up, and told him to drink the potion because it would be good for him. "Duh, okay, Danny," said Brian unquestioningly, having long since regressed from the moment of relative lucidity that had allowed him to remember being an elf, and drank up.
There was a flash of light. Brian's huge, hulking body seemed to melt away, and for a moment Danny was terrified that he had somehow gotten the potion wrong and accidentally killed his lover. But as the magical light faded, he could see that he had been successful, for in the place of the gigantic, muscular human farmhand there stood a slender and intelligent-looking elf, still in the farmhand's ragged clothes which were now much too large for him. Danny didn't waste any time, running forward to throw his arms around the new and improved Brian (shorter than Danny for once) in a hug. "Oh, Brian, I knew there was something more to you! Something smart, underneath everything! I knew I was right to love you!"
Brian stood there awkwardly accepting the hug without returning it, trying in confusion to work through his thoughts. He had gotten used to the dull, simple thought patterns of the farmhand, but now his brain was working at a million miles a minute. He wasn't thinking like a human at all, he was thinking like an elf. He felt like an elf. The experience of being transformed into the elf, transformed into the farmhand, and then transformed back into the elf again had done something to him. He could sense that he now had magical powers, or that latent magical powers he had always had, as an elf at least, had been awakened. He felt no attachment or even gratitude to this human who was in love with him and who had rescued him, and only thought of how he could use him for his own ends. He knew that Danny's potion wasn't powerful enough to break the spell over him permanently, that he would revert back to the farmhand if stayed here without doing anything, and knew that he had to use Danny to break free.
"Yes, my love, you have freed me from the curse," Brian smiled lovingly at Danny. "Through all my days of toil I always knew that you would grant me release."
"I know another way to grant you release," Danny grinned suggestively and groped at Brian's crotch, which disappointingly had much less of a bulge. Brian shuddered, and it took all of his willpower to keep from incinerating the insolent human right there, but he needed some way to transfer his magic to Danny and this seemed like the easiest.
"...Yes. Of course." Frowning, he yanked down Danny's pants. "Bend over." If he had to be with this filthy human he wanted to get it over with as quickly as possible without wasting time on foreplay or romance.
"Someone is eager," Danny teased as he complied. Apparently not everything had changed! He gasped out of habit as Brian entered him, although his new equipment was much smaller than the titanic cock he was used to, and the thrusting much less passionate, like he was just trying to get through it. Which, of course, he was - Brian was sickened by the thought of lying with this human, and had to use a spell to keep himself hard and bring himself to climax as soon as possible.
Danny stood up and smiled, trying to hide his disappointment with the fuck. Once again he hugged Brian, and whispered to him, "What should we do now? My father is coming back, we can't just stay here like this."
Brian sensed his seed inside Danny and knew that the magic would work now. He could have done it with a mere kiss, but saliva was much less potent than seed and he didn't want to take any chances. "I agree," he said, and cast his spell.