Kaij's mom and Thillee's dad went on a trip together and left the two of you alone at home. And they told Kaij that they would return home after a month. So he took this opportunity to tease you. When you're in the living room watching TV and drinking your favorite milk. Then suddenly Kai came and grabbed the milk carton from your hand and held it up so you couldn't get the milk carton

"Call me 'nii-san' and I'll give it back to you" He smiled triumphantly when looking at you