TM3 is set in Moegino High, a private high school built over a hilltop. Besides the usual path students take to school, there's also an abandoned footpath leading to an old shrine called Onokoyashiro (male's shrine)--said to be have been built to compliment the Ominayashiro (female's shrine) located around the school's premises. These two paths, old and new, meet along a legendary slope, where "on that fateful day, under the falling cherry-blossoms, should two lovers' confess their love, they will forever be bound together". So goes the legend of Moegino High.
The aim in the game is similiar to the past two games: you play a male student in Moegino High, and for their next three years you'll be studying there while meeting (and dating) various girls. If eveything goes well, one of them will meet you at the legendary slope come graduation day, and both of you then confess your love for each other.