The main characters of Tentai Kansoku are seven friends that met at college while in the astronomic observation club "Sagittarius." Being in the club was just an excuse for them to go to the beach in summer, and skiing in winter. Actually, the only time they ever observed any stars was at summer camp during their senior year.

Dreaming of a bright future, the seven exchange vows for eternal friendship. However, over the next several years, their busy schedules cause them to begin drifting apart.

It's been three years since that summer when they laughed together gazing at the stars. Will their friendship continue to drift farther and farther apart? Or will they manage to strengthen their friendship again?