Sigulll's activites

Shin is barely making ends meet, hustling as a rogue mechanic on the mean city streets. Problem is, ...

Alan meets Hayden, a free-spirited youth one night. The pair hit it off, but Alan's new feeling...

"Shizuki-kun, you're not good at breathing." Jun Shizuki, a hedonistic womanizing sax...

I’ve been searching for this kinda old shoujo comedic manga where the MC is super smart but also knows how to have fun. She transferred to this super strict school where everyone else is basically depressed there, she eventually became the student council and changed how everyone studies.
She also have a boyfriend for more details.
Does anyone knows what manga this is?? because that manga was my childhood but I forgot the title Thank you in advance( ´∀｀)