It started like any other day until you turn around...
Nanakusa Mihoro, 2nd Year of High School a big sister with big responsibilities...
Miyao Chiei, First Year of High School the man that so happen to turn around.

It’s been little over a month since the first semester of high school started. Shinobu runs into her classmate, Okachimachi, in the art room and tries to start some small talk with him. However, she was met with a cold and emotionless response. The next day, Shinobu runs into Okachimachi in the infirmary and finds out a surprising secret that he has been keeping, both of them…

(Source: Mangadex)

In her first year of high school, Urara Andou fell in love at first sight with the kind stranger who saved her on the train. Too flustered to ask for his name or contact information, she swears to take action the next time she falls in love. But it turns out he's a senpai at her school!? Reunited, Urara believes it must be fate. But before she can take action, his childhood friend Misono-kun tells her "I won't hand Aiji-kun over to you." What will she do?