Atsu is the childhood friend of
Karin,
Jun,
Yume,
Yurari and
Seiji and later the friend of
Mitsu.
She is the head of the student council and is known for her rigor and severity. Because of her duty, she doesn't drag much with Karin and Jun, the distance is created between them and that makes her uncomfortable.
She looks extremely cold at first glance but in reality she is very kind and that is one of the reasons that explains her popularity. She is far from indifferent when she learns that Seiji is back, however she can not spend much time with him but she still finds a way to go to see him from president of the council to club president.
(spoiler hidden)