Steven Universe

In Steven Universe, the world is protected from evil by the Crystal Gems, a group of intergalactic warriors who draw their power from special magical gem stones. The four Gems are Garnet, Amethyst, Pearl and Steven. Steven is a boy who inherited a gemstone from his mother, a Crystal Gem named Rose Quartz. As Steven tries to figure out the secrets of his gem, he spends his days in Beach City doing activities with the other Crystal Gems, his father or other humans, whether it's helping them save the universe or just hanging out.

Throughout the first season it is slowly revealed that the four Crystal Gems in Beach City are the remnants of a once great interplanetary civilization of Gems. Most of the locations visited by the Gems are ruined shrines or locations that were once of great importance to Gem culture, but have become derelict and fallen into disrepair during thousands of years of neglect. The second half of the season deals with this theme in greater depth, revealing that the Gems are cut off from their home world and that the monsters and artifacts they encounter throughout their adventures are actually Gems who have lost the ability to maintain rational humanoid forms. In the last few episodes of the season, it was also made clear that the plans of the "Homeworld Gems" for Earth and its inhabitants were not benign — and that after 5,000 years their attention is once again drawn towards Earth. This is expanded upon with the introduction of two new characters from the invading Gem home world: Jasper and Peridot. It is revealed that the Crystal Gems, led by Rose Quartz, rebelled against the machinations of the Gem home world and won, but remained on Earth as both its protectors and as exiles. (source: en.wikipedia.org)