Kotoko falls off her bike. She's literally stupid. She cannot even ride a bike the correct way without getting hurt, and then she always makes a show of crying and getting everyone's attention.
Yuuki never ever does things like that. He brings no trouble to anyone, and he does everything perfectly. He is happy to be the opposite of Kotoko, the one to have done everything perfectly, the one who is deserving of all the positive attention.
He is distraught when Mama blames him for injuring Kotoko, when he'd done nothing but stay far away from her.
"Thank God you had your helmet on, Kotoko," Mama says, rubbing Kotoko's back. "Things could have been terrible if you hadn't."
Kotoko nods, teary-eyed. She looks very small on their couch, her leg raised onto their center table. "I never forget to wear a helmet," she says, uselessly.
"There's no need to praise basic knowledge," Naoki remarks, frowning as he hands Mama the First-Aid kit. Naoki turns back to Yuuki, walks towards him. "Kotoko's ruined Yuuki's fun."
"She's the worst," Yuuki tells him, letting Naoki led him out the living room. He ignores the way Kotoko sulks behind him, ignores Mama's murmurs of dissent. "Will you bike with me instead, Naoki?"
"Sorry, Yuuki," Naoki replies. "I'm going to take a bath. Let's go later."
Yuuki bikes alone, glances both ways when he crosses the street. He should bike far away from the house. Mama is always too preoccupied with Kotoko these days, and Naoki is too busy. No one would miss him.
Besides. He hasn't even done anything. It's all Kotoko's fault; she'd been the one to ask to go racing in the first place.
She's so laughable, getting hurt and losing.