Sawako Sera

Sera has the ability to enter reflective materials(mirrors/marbles) mentally, while her body stays in the real world. She has a strong sense of rule abidance which causes her a lot discomfort from her class mates. She believe that as long as she abide rules she keeps something perfect/beautiful inside her.

Background
Sera had lived under the philosophy that well behavior was what could be considered "something beautiful" in a person because of her school teacher. Because of this, she was always a model student who never broke the rules and also pointed out their wrong actions to those who did. As a result, Sera earned the nickname "Miss Perfection" by her school classmates who also stopped wanting to hang out with her.

When Sera entered high school she still believed in her philosophy about well behavior but questioned herself if it was smart to continue that way, due to the way others treated her in school. It seemed to her that people who broke rules "enjoyed life more". On spur of the moment she tried to miss the entrance ceremony but later regretted that decision, because she felt that by abandoning that ideology, she no longer had "something beautiful" inside her heart.

For this reason, Sera subconsciously activated her power and entered the reflection of the marble. As indicated by the clock hands in the reflection, that still didn't reach the time of the entrance ceremony, Sera wanted to flee to a world where she never broke her own rules and remained pure.

After doing some research about Sera's past and her actions the day she used her ability, Kei figured her personal crisis and also noticed that she thought about breaking her own rules by eating a candy at school. To avoid Sera from getting into the marble again and help her with her doubts, Kei made Haruki use her reset ability and then took the marble from the street. Then made Sera believe that she broke her own rules for a moment(something that made her cry), but Kei revealed that eating sweets was only forbidden if you do it during the class and not in the school itself. He told to Sera that he also believed that it was a good thing to follow rules, which made her feel relieved to know that she didn't brake the rule and thus still had "something beautiful in her heart". She also realized that her way of thinking wasn't something she really wanted to abandon.