The Suspicious Black Underwear - S1.E7

Yuzuru notices that Kiri and Sachi are getting along very well. Because of that, she gets jealous and thinks that Sachi could become better friends with Kiri than she is with her. She starts to act strange towards Sachi and Kiri. It turns out that Sachi was helping Kiri to pick a birthday present for her. Afterwards, all of them (together with Kanako, Masturika and Mariya) celebrate Yuzuru's birthday.