A Gyoza Party with Friends Episode 6

Tsumugi wants to throw a party: a gyoza party! And a party means that she can invite all her friends, everyone she knows at daycare, and Kotori, and Shinobu, and even Yagi! But she's just a little girl, and doesn't know that you have to get permission from Kotori's mom before you can hold a party at Kotori's house. How can Kouhei resolve this sticky situation? And what's the best way to make gyoza, anyway?