Yuki's teacher Jun Inoue, passes his test answers around the class as punishment for failing the recent math test. This forces Yuki to seek math tutelage from Kaori, who happily agrees and takes him, Shogo and Saki over to her house that evening to study. At Kaori's house the group meets her cheerful mother Shiho Fujimiya after which they settle down to work, with Yuki and Saki making slow progress...