When something new begins, it tends to do so suddenly and unexpectedly. Returning from the countryside on the bullet train, a girl, Kurohime Yuuhi, is assigned the seat next to you. You learn that a cousin you have barely spoken to, Himiyama Rei, is going to be living with you. These two encounters, along with your childhood friend, Tsutamachi Chitose, who lives next door and is older than you, will, like the changing color of the autumn leaves, bring color to your heretofore unchanging life. A chance encounter creates a beginning. A relationship blossoms from a distant connection. A friendship becomes something more. As autumn deepens, you start to feel like you may just fall in love.