Punishment Box Productions

Serena has a student

   "UNCLE ACNO!" Izuku cried from downstairs. The poor tired dragon king got up and walked downstairs, muttering angrily about his lack of sleep nowadays. 

   "What is it now, Izuku-" Acnologia stopped in his tracks as soon as he saw the problem. "Oh. There's another freaking portal in the guild hall. When will you guys ever learn?" 

   "Gray accidentally made it while teaching Shoto some ice devil magic. Nobody seems to be able to get rid of it, and it doesn't seem to be sucking anyone in or spitting anyone out." Tanjiro stated, Nezuko nodding in agreement beside him. 

   Acnologia sighed. "Right, let's see if I can destroy it then, huh? Okay, stand back everyone." Once everyone backed up, Acnologia blasted the portal with a beam of magic. Fortunately, the blast did not destroy the guild hall. Unfortunately, the portal was not destroyed either. Instead, it absorbed the magic and started glowing bright blue. 

   "Uh oh!" Gon exclaimed. "That doesn't look too good!"

   Killua shook his head. "Definitely not." 

   Then three people flew out of the portal in rapid succession, and the portal promptly vanished. All three people hit the floor. Hard. One began cussing loudly in Russian. The other began crying. And the last one cheerfully stood up and smiled. "Hi, where are we?" he asked in a strong Russian accent. 

   "This is the magic guild Fairy Tail!" Serena exclaimed, appearing out of nowhere. 

   The one that asked the question gasped. "Magic? What kind of magic is there?" 

   Serena shrugged. "There's many magics out there. Let's start with my magic. I have glitter dragonslaying magic-"

   "GLITTER? I want it! Can I learn magic?" the man gasped again, blue eyes sparkling. 

   "Sure!" Serena grinned. Acnologia, hearing this, inwardly groaned. 

   "We're joining this guild, Yuuri and Yurio! Come on!" the excitable man exclaimed to his two buddies who were still lying on the floor. 

   "I don't wanna get up..." moaned the crying one. 

   And so Yuuri (the crying one), Yurio (or Yuri. Yurio was his nickname), and Viktor (the excitable one) all joined the guild. Of course, they all picked up a type of magic. Yurio learned transformation magic with Lisanna, deciding to focus on transforming into different types of felines. Yuuri learned ice make, just like Shoto did, but he learned the dynamic type with Lyon instead of static ice make with Gray. And true to his word, Serena did end up teaching Glitter Dragonslaying magic to Viktor. 

   They were not the only ones training hard, however. By now, Shoto had completely mastered Ice Make, and was now beginning to learn Ice Devil Slaying magic. Rody, the Sun God Slayer, and Tanjiro, who made use of Sun Breathing, trained together because of their common element in the sun. 

   Meanwhile, poor Acnologia became more and more frazzled by the day. If he had thought the guild was chaotic before all these newcomers arrived, then this was a nuclear warzone. Of course, he welcomed them all with open arms (yes, even the dude called... what was his name? Victuuri? Well, the guy that Serena transformed into a mini-him), but he did have some preferences, like Izuku (because favoritism amirite?) and Levi (because he cleans up after everyone). 

   Sighing deeply, Acnologia picked up his coffee cup, bringing it to his lips to take a well-deserved sip. Then suddenly, a blur of pink, white, and black crashed down on him. Coffee? Everywhere. Expensive mug? Shattered. Acnologia? Crying. "Punishment Box Productions for you!" the exasperated dragon sobbed, dramatically pointing up to the two newcomers sitting on his back. 

   And that is how the Fairy Tail guild got the opportunity to watch a tattooed man and a blindfolded dude dance to the Sailor Moon theme in pink cat maid outfits. 

(A/N: this is the result of watching one anime, writing half the chapter, watching a second anime, and finishing off the chapter. Hope you enjoyed the chaotic energy from this chapter!

Also I may or may not add another Demon Slayer character next chapter.)