When they learned Karkat had said yes, the first thing Dave and Eridan did was break into a victory dance composed mostly of whipping and dabbing (and more dramatic posing on Eridan's part).
"You guys have issues," Karkat grumbled, shaking his head.
"Tell me about it," the guy next to him replied, still staring at his phone and furiously texting.
After Nepeta started joining in and yet another one of the hosts kept protesting ("This behaviour does not behoof a member of royalty, Nepurrta!") the three finally stopped their imitation-dancing, and Eridan ran his fingers through his black-and-purple hair, announcing,
"Vvery well then, Eq! Wwe shall noww begin the introductions! I am Eridan Ampora, the Prince Charmin' type!"
Dirk, Dave, and The Texting Guy chuckled at this, and Eridan hissed, "Shut up!"
He cleared his throat, then continued, "You'vve already met the Strider twwins, who are the Stoic, 'Brotherly Lovve' types."
"Where I come from, that's called Incest." Karkat deadpanned.
"Wwhatevver, that's not the point. The blonde one who's always textin' is Sollux Captor, The Sexy A$$hole Who Gets All The Girls type."
Still glued to his phone, Sollux added, "Guilty ath charged."
"I knoww it's annoyin, but ignore the lisp," Eridan whispered.
Sollux finally looked up so he could flip the other Host off and scowl, "F*** you, Ampora! No-one careth!"
Dave nudged his twin and asked, "Remember that one time we tried getting Sollux to sing Kyoto A$$? Look at dat ath ath ath ath ath ath ath--jegus, I'm kidding," he mumbled, seeing Sollux's glare.
Dirk tapped Karkat's shoulder and whispered, "Eridan and Sollux have a long-lasting rivalry going on, so all of this sh**'s normal. They insult eachother about everything."
"I wasn't offended."
"Just letting you know."
Eventually Eridan and Sollux quit bickering, and the former said, "Anywway! Point bein', Sollux is an
@$$hole. This is Nepeta, the Shota Version Of An Old Obsessed Cat Lady type."
Nepeta narrowed his eyes and said in a lowered tone, "Ampurra, I thought we agreed we'd stop the Cat Shaming."
"Cats suck, you should'vve picked fish." he said confidently, trying and failing to look smart by adjusting his hipster glasses.
"Fish aren't cute!" he exclaimed with a tone of despair.
The same host who talked to Nepeta earlier came over and patted him on the shoulder, saying, "Nepurrta, calm down. He is still our leader and must be respected,"
"How did he become the leader?" Karkat muttered in disbelief.
"It was his idea, so we thought it'd be only fair to let him run this dog and pony show." Dave said.
"That'th literally the only reathon why." Sollux added. "We can't kick him out."
"You can't," Dirk corrected.
"Anywway! Nep is the Shota type." Eridan continued. "Eq ovver there is the Tall, Sweaty type Who Is Obsessed Wwith Mackin' Up To All The Other Rich People And Anyone He Considers A Person Of Authority."
"Don't say that about Equihiss!" Nepeta exclaimed. "That's rude!"
"Wwhat? I'm bein' honest."
He folded his arms and shook his head, saying, "Mew're just in a nasty mood, aren't mew?"
Eridan ignored his question and asked, "Are there any other introductions needed?"
"Nah, that's everybody." the Striders said in unison.
"So...what form of mental torture are you subjecting me to now?" Karkat asked.
"Wwe decide your type. Wwhat wwould you prefer?"
"Is there room for a Brutally Honest type Who Blesses This School With His Eternal Flames Of Rage?"
Eridan thought for a moment, then said, "Nah, that's too similar to Sol ovver there. Try somethin' else."
Karkat repeated, "The Guy Who Blesses This School With His Eternal Flames of Rage type?"
"You wwon't get customers with a type like that. Does anyone else havve ideas?"
"Tsundere type," Dave piped up.
"Angry on the outside, fluffy on the inside." Dirk finished.
"Do I look fluffy to you?" Karkat growled, but before he could start a rant, he was drowned in the approval of the other members.
"We could use a tsundere!"
"The Facebook poll ith thaying yeth."
"If we have a tsundere, we could finally be a real animeeee...!" Nepeta gasped in awe.
"It's official!" Eridan announced. "Starting today, you are the Tsundere Host!"
"Starting when?"
"I said today, commoner."
"Idiot, I'm asking what time today?"
"Oh! ...After school, same room. Don't be late!"
The bell for lunch rang, and all of the Host members went to leave, except for the Striders and John (who was cleaning up the remains of the now-forgotten vase).
Karkat immediately turned on Dave and demanded, "Tsundere? A f***ing tsundere? What on Earth compelled you to believe I would ever want to be a two-faced, blushy anime stereotype at all, much less on a daily f***ing basis?"
"I could tell Bro was thinking it," he said, shrugging nonchalantly.
Karkat turned to Dirk and asked, "Why were you thinking that?"
"You got excited when you asked if it was like a harem, and I took a wild guess. Looks like it paid off,"
"That was not f***ing excitement!"
This time, it was Dirk's turn to shrug indifferantly. "Fine then. What was it?"
Karkat opened his mouth to make a retort, then realized he couldn't think of an excuse.
"I'm just here to practice acting. That's it."
"So? Being a tsundere is a great opportunity in that case. You can be yourself as long as you apply some filters and self control, and then when the situation calls for it, you can practice your acting."
"You expect me to know when I'm supposed to swap attitudes?"
"If you're genre savvy, you should be able to pick up on this sh** really fast. So fast, Sonic'll be left in the dust, with all his 'gotta go fast' memes lost to the wind. The wind just groans--it's used to having stupid sh** lost to it. Those animal balloons belonging to all those depressed, creepy clowns; all the desperate cries of cheesy romance characters...you name it, the wind's had to deal with that bullsh**."
"You're making me feel like the wind." Karkat interrupted flatly.
"What he's trying to say is that you should think of it in terms of being in some kind of romance movie." Dirk said. "Surprise the girls with some flowers, pour tea, ask them how they're doing, give compliments...sh** like that."
"So all I have to do is try balancing myself with the personality of the dream romcom protagonist."
"I would recommend being yourself the whole time--"
"--but nicer. Sollux does it, so you can manage too." Dave concluded. "You'll figure it out."
"If you want advice or help at any time, don't be afraid to ask."
"This is stupid." Karkat sighed. "I'm getting lunch."
"See you, then." the two said in unison.
John looked up from his broom and waved. "Have a nice day!"
Karkat ignored them and just hoped he'd be able to find one of the cafeterias before his next class period.

----------------------------------------------
A/N:
So the character sheet goes:
Haruhi - Karkat
Tamaki - Eridan
Hikaru and Kaoru - Dirk and Dave
Mori - Equius
Honey - Male!Nepeta
Kyoya - Sollux
John will also appear, but he has a role outside of the original Ouran cast.

...This seemed less random in my head.

Anyway, as said in the description, criticism and ideas are always welcome, and thank you for reading!