As a joke, Kamui pretended to hate Emi and she went along with it.
"Kamui-san..." His two little friends said.
"When did this happen?" Miwa asked, raising an eyebrow.
"Poor Emi..." Misaki said, sympathetic to Emi.
"Kamui-kun! How could you make Emi sad?" Aichi asks Kamui, concerned for his sister.
"..." Kai says. 'thank goodness, I don't need to hear his annyoing mouth going gaga over Emi...'
"Kamui's mine!" Nagisa comes from nowhere.
"Emi... Are you okay with this...?" Shin curiously asks.
When Kai finds out it's a joke, he says, "I knew it was too good to be true." 'NOOOOO!' (in his mind)