Aneiro

We won't let you off the hook until you've fallen for your big sister's charms☆
"It really brings back memories," sighs the protagonist, Hibino Wataru, who has just transferred to this school despite his young age.
It's only natural he'd feel that way, though—years ago, his parents' work forced the family to move abroad, and he hasn't been able to return even once since then.
But that's not the real reason. The truth is—
He's finally going to be reunited with his close older sister, Hibino Kaoruko, and his childhood friend who's like a sister to him, Kunugi Eina.
When he moved away back then, both Kaoruko and Eina were attending full-boarding schools.
Wataru, however, needed a guardian to look after him, so he had no choice but to leave. But now...
"I finally get to see them today."
There's Kaoruko—older but laid-back and caring—and Eina, who's competitive, stubborn, and even more sisterly than his actual sister.
"Wataru-kun!" "Wataru!"
Sharing the joy of reunion and the emotion of the moment, their lively days together are about to begin—
Or so it seems? Probably?? Maybe???
The catch? Right after entering school, he quickly discovers that these two are actually—
'Saint of Science Devoted to Science' (Science Club: Kaoruko)
'Emerald-Eyed Witch of Insight' (Astrology Club: Eina)
The two are so hopeless they're beyond words, yet they're famous (?) for one shared trait: they're troublemakers!
Not only that—after reuniting after so many years, they're naturally all over him every day, making it impossible not to draw attention!!
The sudden chaotic school life is already dizzying, but just when one wave settles, another rises!
Student Council President Washimi Sayaka sternly announces:
"If you don't produce decent results by the end of this semester—that is, at the student assembly—your clubs will be disbanded!"
As far as causing commotions goes, their clubs are certainly impressive, but when it comes to results worth showing off, sadly, they have none.
It would be much easier to stay out of it, but seeing the two of them look up at him pitifully and beg, "Let's work hard together," he just can't bring himself to run away.
Will their clubs end up being disbanded? And what kind of scenery awaits Wataru ahead?