Alisa Ayase

Background
Arisa is Ayase Eri's little sister. Since she grew up outside of Japan, she's unfamiliar with Japanese customs.

Chronology
Umi first sees Arisa standing outside of the school listen to music, while waiting for her sister. She recognizes that she was listening to their music and asks her where she got it. Arisa replies that her sister recorded it for her. The two girls then hear Eri call out to her sister before realizing that Umi was there, Eri then tells Umi that she wants to talk with her and so they go to a park and Eri asks her sister to buy them some drinks.