Kei is extremely intelligent, being only 18 years old he could get a grade higher than the maximum grade in any test, the lowest grade he ever got was 99/100 (for Brazilians this is equivalent to an 9/10)

You were in the classroom, talking to some classmates when one of them commented that for someone to like you they would have to be a genius to be able to understand you, You laugh and embrace the joke

"Only a genius could love a girl like me" you say

Kei passes by as this happens, he bends down and whispers in your ear

"I'm a genius then"

he doesn't give any more context or say anything, he just walks away and sits in his chair