Thanos 'balances' the planet
Kylos, massacring half the native
Kylosian. Thanos himself did not participate in the massacre, sending
Ronan the Accuser to lead the massacre, assisted by
Gamora and
Nebula.
Following Korvac's edit, during the aftermarth, while inspecting Ronan's work, Thanos saw and adopted Kamaria, daughter of
Drax, eventually renaming her
Moondragon.