The plot of Steven Universe, as gleaned from my Tumblr dash:
Pink gem lady comes to Earth and falls in love with a human. She gives birth to a half-gem-half-human baby but dies in childbirth. Some more gems come to Earth to raise the child. (They can split into two and fuse into one somehow?) One of them is stuck at the bottom of the ocean. Also there are some evil gems. Wacky and sometimes sad hijinks ensue
Well the gems (all fourish of them) came to earth way before Rose met Greg and they basically stopped their culture from taking over the earht. But they stuck around to contain gems that got damaged and corrupted on Earth to protect the Earth. Flashforward a few millenia and Rose meets Greg, falls in love and has a baby with him.. She didn’t actually die so much as gave up her physicall form and combined with her son Steven. Greg and the remaining members of Rose’s rebellion team (Garnet, Amethyst and Pearl) than had to raise Steven to both be a human child and a gem. All three of them are heavily implied to be outcasts on their own planet. At the mid-point of season 1, one of the corrupted gems, Lapis, wakes up. She’s super pissed at Garnet, Ameethyst and Pearl, but than Steven heals her and she just kinda of flies back to their home planet. In the second half of season 1, hommeworld gems start looking at Earth, leading to a confrontation at the end of the season.
Garnet is a fusion. All gems can fuse with other gems, to do battle or have sitcomesqe hijinks in one case, and Garent can fuse with other gems herself. But she herself is a semi-parmanent fusion between two gems who are a romantic couple -ruby and sapphire. It is implied this was the reason she was an outcast on their planet.
I think you’d like. Rebecca Sugar wrote and storyboarded a lot of Adventure Time episodes before she left to create Steven Universe including What Was Missing, I Remember You and Simon and Marcy (which was her very last episode I believe).
I think I’d like it too! I LOVE all three of those AT episodes you mentioned. I definitely will watch it at some point, it’s just a shame there isn’t a way to do so legally here, as far as I know. :( (Not that that’s much of an obstacle, but still.)