Midori Hamanaka has a crush; the object of his affections, a girl he always sees in the train on his Friday commute to school. He wants to properly greet her to start up a relationship with her, but he ends up selling himself short and doesn't follow through when actually at school. To get over this aspect of himself, he starts to repeatedly practice saying "good morning" to her when he thinks he's alone.
On another Friday he doesn't talk to her again on the train, but an unexpected rain shower comes and he's left with no umbrella. The girl, approaching him, gives him her umbrella and goes to share an umbrella with her friend. This marks the first real time the pair speak to each other, even if it was for a moment.
Next time he sees her, Midori is prepared to give back the umbrella and talk with her more, but the song ends before he can actually say anything to her. He resolves not to leave it at just there though, and wants to work up to meeting with her on Sunday.