Sometime before the Tenrou Island arc...
One of the unspoken rules of Fairy Tail was that after you got trashed at the bar, you didn't go outside for a while. You were supposed to pass out, be tucked away on a table or on the floor by anyone still sober, and ride out the night until the guild re-opened when the cleaning and carpenter crew came in the next morning.
Part of this was lax enforcement of the legal drinking age within the guild. Within its walls, Makarov was officially the guardian of everyone who had been adopted as an orphan, and he loved defying the local Magnolia civilian government just as much as he loved defying the magic council. So anyone was allowed to drink, so long as they stayed within the walls. Cana had started when she was just fourteen, and had been building up her impressive tolerance ever since.
But the other reason everyone was supposed to stay inside was because most people lost control of their magic after a certain point of intoxication.
Cana was an exception to that rule. She had obtained her MUI permit - Magic Under the Influence - as soon as she turned 18, turning into the complete and total officially sanctioned lush that she was. The test had been extensive, and as a result, she was not only pretty much allowed to drink with impunity anywhere she wished (because she had proven she had total control of her magic even on the verge of alcohol poisoning), but she had gone to the next level and become certified in teaching MUI classes for those caught in violation of the laws. It was a good way to pick up extra money on the side.
She never, ever thought that she was going to have to use that knowledge on her own guild.
She stared at the collection of hungover, pitiable mages in front of her. The party the night before had been one of the biggest drunken bouts in Fairy Tail history, and that was saying something. When the party had gone outside in the town due to someone's great drunk idea, the parade of carousing mages had accidentally lain waste to a bridge, the church, the park, and a few other local landmarks. No one was injured, but that was pure luck. They'd have to pay the town for the destruction out of their wages, as usual, but the entire incident had brought Fairy Tail under questioning from the local government as well.
MUI was illegal without a permit for a reason.
"Lucy," she said, and the stellar spirit mage looked up quickly, then down guiltily when she saw Cana's accusing finger. "You ended up drinking a beer followed by four shots of tequila. You vomited all over Natsu's shoes. What rule of drinking did you violate?"
"Beer before liquor, never been sicker," Lucy quoted miserably. She was still faintly green. It was always a harsh lesson. "Liquor before beer, you're in the clear..."
The angry finger went to the next guilty mage at the table. "Gray! You drank twenty beers. Twenty! Wendy had to use emergency healing on you because your pulse had dropped to critical levels!"
Gray scowled at looked away.
"How large is a single serving of beer?"
"Sixteen ounces," Gray muttered.
"And how much alcohol is in it?"
Cana sighed. "No. The answer is that it depends on the beer. Some of the high gravity ones approach two ounces. You almost died, Gray."
Gray had the presence of mind to join Lucy in looking at his feet.
"Juvia," Cana said sharply, and the water mage cowered under Cana's glare. "I don't even know how it's possible for you to get drunk, but rumor has it that you 'took advantage' of Gray's comatose state after Wendy healed him."
"J-Juvia did no such thing!" she protested, but blushing as she stole a glance at an equally blushing Gray. They'd woken up in a rather compromising position that morning, Gray muttering about being cold and wet.
"Everyone saw you snuggling him like a teddy bear for hours. Remember, if they're not conscious, it's not consensual."
Cana rounded upon the next victim. "Natsu! You let Happy get drunk!"
"It was a party," Natsu said defensively.
"Happy is six and he's a feline. Exceed. Whatever." She waved her hand in annoyance as she tried to get the right word. "Alcohol is poisonous to cats. He can eat fermented fish, but not fermented grains. And you had eight flaming shots yourself, which you proceeded to throw up, on fire, on the elementary school playground."
Natsu stared at the ceiling, but then burped a small spout of flame. He had the good graces to look embarrassed, even as Happy patted him consolingly.
Erza held up her MUI permit silently, and Cana sighed. "Yes yes, you were designated to keep control of them last night. And you didn't." Cana crossed her arms across her chest. "You know you can get your permit suspended for that, right?"
It was quite possibly the first time in Erza's life that she looked ashamed.
"Mirajane! I know you love making everyone happy, but the law says you should not serve someone who already looks intoxicated. Which was everyone."
Demon Mirajane smiled innocently at Cana, her eyes glittering within her angelic face. "Including you?"
Cana glared at her through narrowed eyes. "If I ever somehow accidentally destroy a building, then yes, even me." She squared herself and put her hands on her hips, giving them one final berating. "It says a lot about your mental states when even Gajeel is doing less destruction!"
"That's 'cuz he'd already gone home to dream about Levy," Happy said with a snicker.
"Hush, Happy," Erza said softly, and the Exceed shut up quickly.
Cana sighed. "If something like this happens again, Fairy Tail will lose its liquor license." For the first time that morning, Cana looked sad instead of angry. "And what will I do if I have to... be sober?" Before the tears could spill over from her eyes, she got a hold of herself. "So! No more drunk magic on the streets! Am I understood?"
"Yes, Cana," they all grumbled in unison.
The impromptu MUI class split up into the normal various factions. Cana found herself sitting at the bar with Mirajane pouring her a nice, plain glass of water. Then pouring one for herself. Everyone was still a bit hungover, after all.
"Maybe you were a little too harsh on them," Mirajane said cautiously, stirring a few drops of lemon juice into her glass.
"Maybe," Cana agreed, and took a sip of water. "But the Master is already in enough trouble with the city." She drummed her fingers on the bar. "Honestly, a level 1 MUI permit isn't hard to get, but it takes a severe amount of control on your magic to hold onto it once you hit the higher blood alcohol levels for the level 3 and 4 ones." She took another sip, and pulled out one of her cards, spinning it idly in her hand. "I'm the only person I know of that actually gets better at magic the more I imbibe."
Mirajane looked off in the distance, an unreadable emotion flickering across her face. "There are others," she said cryptically, but did not divulge further information to Cana.
"Tch," Cana said, then downed the rest of her water in one go. "Ne, Mira, give me a tequila sunrise. I need some wake up juice."
"Coming right up," Mirajane said sweetly to the guild's resident lush.
A/N: A minor fic format rant about some of the wildly inaccurate statements regarding alcohol I've seen in FT fics. I'm a real life Cana, but even I'm ready to vomit after 5-6 beers or a bottle of wine. (And trust me, vomiting up alcohol at 3AM in the bathroom of the 24 hour burger joint is one of the sorriest places you can find yourself...) Drunken antics are fun, but please don't encourage alcohol poisoning. Keep the number of beverages your drunken FT compatriots consume to reasonable numbers, and when they do over-indulge, keep them INSIDE the guild!