i do not get it can someone explain the story to me?
My attempt at explaining: the middleschooler MC, Rui, has been developing romantic attraction for Reina, ever since Reina transfered to her class in elementary school. But Rui has yet come to term with the posibility of dating someone of the same sex (she's still very young), so she has been stewing the confusion in her head, and the occasional confessions Rui received from girls get rejected due to that confusion, too. One day Reina start dating a boy, thus Rui is sad and goes to sensei, whom Rui knows to be lesbian, for counseling. They have sex and talk, Rui comes to term with her sexual orientation and that she wants to be with Reina.
The next day, the girl, whose confession got rejected by Rui previously, makes another attempt. Rui ponders giving her a chance, though she looks at Reina and says "just kidding". What this means is up to the readers' own interpretation.
Hope that helps.