Watashi no Shiranai, Senpai no Hyakko no Koto

A senpai and his kouhai had no contact in the past except for using the same train station to go to school, thus only meeting each other in the morning. One day, they made a promise: "A single question each day, and answer it honestly." "I want to know more about Senpai, and I would like to know what I don't know about Senpai. So let's ask each other one question a day—for a total of 100 questions." This is the story of two people who are slowly getting closer, one question a day. (Source: Kadokawa, translated)