Choushinsei Flashman

In 1966, five children were kidnapped by aliens and taken into space. However, they were saved by the Flashians, and raised in the Flash system, training constantly so that one day they might return to Earth if it should ever fall into trouble again. One day, the five of them, raised as siblings even though they aren’t biologically related, receive word that the Reconstructive Empire Mes is going to Earth. They rush to Earth, in the hopes of not only stopping Mes, but also maybe finding their real families along the way.