"Yay! I'm gonna be in highschool~ I'm gonna be in your school~ I'm gonna look cool~ cooler than my no jam bro!" Chaeyoung rapped and ended it with a dab. It irked her older sister,

"Would you shut up already, cub? You've been repeating the same thing for weeks." She shows her look of disgust in which the younger replied with sticking her tongue out.

"You're on your senior year now, unnie! So old."

"Ya! Chaeyoung!"

Their days were always like that. They would laugh for a reason as light as a feather. 

Due to both daughters going in a private school, their parents decided to work abroad to sustain their needs. Jeongyeon independently took care of her younger sister at the age of 11, to some it might be a burden, but it doesn't bother her. Watching Chaeyoung grow would always be an ethereal view for her, she's proud that her sister turned into someone people admire because of her looks, talents, and good manners.

And now she's going to be a high school student, no one's more thrilled than her. Now that they're in the same school again, she can take good care of her

But,

It wasn't going to be as smooth as she thinks it will be. She forgot about one small little detail- Im Nayeon.

She may not look like it (because of the cute bunny teeth), but she's trouble, an epitome of it. A whisk of cuteness, a whirlwind of hotness, a pinch of Rumplestiltskin- all in one pale skinned body.

(Well, the Rumplestiltskin part was Jeongyeon's view because of what Nayeon offered)

(JYP High)

"What's wrong with you unnie? You've been glancing around for almost the whole lunch break."

"Nah, I'm just exercising my neck." The older one replied, cold sweats forming on her forehead.

"Yoo! Long time no see!" Jeongyeon's fear came into realization as she heard the bunny's voice "Ooooh, and who's this little chippy? Lil bit too young for ya."

"Uhhh... She's-"

"I'm Chaeyoung, her little sister." She was cut off by the small one.
Nayeon studied Chaeyoung for a moment, then smiled at her as if she's the happiest person upon meeting her. She smirked at Jeongyeon then patted Chaeyoung's head. 
"Wanna have some fun with me, Chaeyoungie?"
"Yeah, sure! I mean how could I say no to a pretty unnie." Chaeyoung grinned
"Ah. But I think Yoo and I still need to talk if it's okay with her for me to play with you."
Jeongyeon sighed with scrunched eyebrows,
"Chaeng why don't you proceed to your class? It's better to be early." She gave her sister a reassuring smile. The younger one thought for a bit then shrugged, she bid good bye to her pretty unnie and her biological unnie.

"Now, what is it that you want Im?" Jeongyeon said rather calmly
"Nothing much, just some things to help me with having remarkable grades."
"Get to the point."
"Quite eager, aren't we?" Jeongyeon rolled her eyes at her "I just need someone to make sure I graduate with boastful flying colors." Another life threatening grin from the bunny.
Jeongyeon just looked at her, she scoffed and shook her head then continued,
"Do my notes, homeworks, projects, etcetera. I don't wanna be tired with life at the age of 18 because of school." Paused only to menacingly grin at Yoo, "You probably know what'll happen to sweet Chaeyoungie if you don't satisfy my needs. You know, Jeong. I'm not much of a patient person."
Jeongyeon gulped and just nodded, thinking only for the best for her sister.
"Okay, fine. But never, ever harm her Im or I back out and you crumble."
"Ah, that's why I like you, Yoo. You're such a fighter." Nayeon said it in a pitiful way, mocking her with a pout.

"We got ourselves a deal, Yoo. I won't do anything to your oh so loved sister and help me pass this hell of a subject" The bunny teethed smugly said, "... And by deal, I mean is, be the shadow behind my breakthrough success in Calculus. Let the world know of Im Nayeon's greatness and beauty!" She smirked and laughed darkly. Yoo Jeongyeon could only sigh in disbelief. She's going through hell for her sister's sake.