The two native peoples of a ruined world, one physical and now extinct through war, the other made of energy, whose surviving members tried to atone for an old mine that killed an Enterprise officer.
The Koinonians are encountered in the Next Generation episode The Bonding. In 2366 an Enterprise-D away team led by Worf surveys the remains of their civilisation, and the archaeologist Lieutenant Marla Aster is killed by a mine left over from the wars that ended it. She leaves a young son, Jeremy.
The planet had been home to two intelligent species. The corporeal Koinonians destroyed themselves in generations of fighting. The others, beings of pure energy, lived on and were left with a sense of responsibility for the suffering their neighbours' weapons still cause.
One of them comes aboard in the form of Marla, recreates Jeremy's home on Earth and tries to take him to the surface. Picard, Troi and Wesley Crusher help the boy face his loss and convince the entity that he must live among his own kind. Worf then takes Jeremy as a brother through the R'uustai ceremony.