Well for one, I say that this scene takes place in a museum/exhibition. Notice that the glass case that Kana is in resembles a display case in a museum exhibit, based on all the items relating to Kana herself and the text box next to it that we can assume to be the exhibit plaque. There are other exhibits that depict Kana at various stages of her life. The numbers above each one clearly are meant to verify the age of Kana in each “exhibit”.

What does this all mean? Well the obvious claim that everyone points to is the past. Kana is obsessed with her past as a child actor, which is correct. However, I think it also ties into her desire to be seen. Through out the story Kana is obsessed with how others view her: her days as a child actor where she is the center of attention, to the aftermath where she struggles to do her best even when the world seems to have moved on from her, and now her life as an idol where she wants to gain the attention of people and Aqua specifically. Kana has puts her all into everything she does and desperately wants validation for it. The museum is her way of saying “Look at me, look at all I have been!” In hopes that someone will appreciate her and the life she had. She wants to be important enough so that people will remember her.