She's Luka's childhood friend who he might or might not have a crush on.
She has a crush on him too and makes pretty obvious hints like 'joking' about getting married or asking be his date to one of their school dances. But Luka is dense as a brick when it comes to that.

She can be a bit Tsun-Tsun to strangers but when she warms up to you she's real friendly.

BTW she needs a name.

Also, she's mad at Luka for stealing her earphones cause they're arguing over which us better, Headphones or Earphones.