"We are the Crystal Gems, we'll always save the day.
And if you think we can't, we'll always find a way.
That is why the people of this world believe in.
Garnet, Amethyst and Pearl. And Steven!"
The short title song of Steven Universe succinctly describes its plot, but here is a fuller explanation of where the show came from, and what it is about:
"Steven Universe" was created by Rebecca Sugar for the Cartoon Network in 2013. Rebecca Sugar came to prominence for her work on Adventure Time, first as a storyboard artist and later as a co-scripter. "Steven Universe" is the first show on the Cartoon Network to be solely created by a female artist. On "Adventure Time", it seems that Rebecca Sugar was responsible for much of the character development that enriched what was a fun, but seemingly nonsensical show. Like Adventure Time, Steven Universe episodes are only ten minutes long, and mix bright colors and quick action with longer plot arcs and subtle character development. For these reasons, it has a wide demographic appeal: young children like the cartoonish humor, teenagers (especially the tumblr faction) like the broad take on relationships, while adults can understand the more mature humor.
The show takes place in Beach City, where a group called the Crystal Gems protects the earth from supernatural threats. The Crystal Gems, Garnet, Amethyst and Pearl, are aliens whose true form is their titular gem, but who project humanoid bodies. Oh: and there is also Steven, the fourth crystal Gem, the product of a relationship between a human rock musician and a Crystal Gem named Rose Quartz. Despite being an alien with great untapped powers, Steven is also a typical boy of about 10 or 12, enthusiastic about toys and games, and just starting to have an interest in girls. Steven is sweet and naive, and his normal growing up process of understanding the world around him is accentuated by the fact that not only does he have to figure out how to get along with cool teenagers, he also has to figure out his place in an intergalactic war. Over the past two years, both Steven, and the audience, are learned more about the background of what is going on around them, something that some characters on the show already seem to know.
The show manages to address issues of family structure and sexuality, while doing it in a non-confrontational way. Steven's situation could be taken to be of a child raised by three lesbians, and although the gems technically are without gender and asexual, they do have a process of merging with each other, forming temporary composite identities/persona, known as fusion. The process is depicted as being somewhat romantic, both in its mechanics (before merging, the gems dance together) and in the emotions involved: gems with an affinity with each other can stay merged much more easily. Although there is many interesting things about the show, the exploration of the entire concept of a single, permanent identity that this has brought about is the one I find the most innovative.
It seems that Steven Universe is going to be produced a while longer, and both the internal intricacy of the plot, and the show's popularity, have room to grow. Along with the popularity of Adventure Time and Gravity Falls, Steven Universe is showing that a cartoon show can be simple, bright, and fun, while still being engaging and thought provoking.