Master of gems is a Steven Universe Sub-Series. It focus' on Steven, the Gems and a new Member, Jack, Who is another Gem who was born a few months earlier, he used his age powers to grow up into a 14 year old. He has two Emerald gems on his feet. His crystal weapon is a Big Sword, He can fuse with Steven to make Jade, His weapon will be a Battleaxe. The crystal gems have found their Arch-Enemy, Onyx, he is the Gem that has been turning all gems into Monsters, His Weapon is a Scythe.
Steven and Jack are waiting for the Big Donut to open, They talk about their gems. Suddenly Lars and Sadie open up the doors, Steven runs in while Jack walks in casually. Steven asks for a Chocolate Sprinkle Double Dipped Donut, While Jack orders a Pizza Donut. While they walk out, Lars jokes with Sadie about Steven and Jack's Mothers, Mad, Jack walks up to Lars and pushes him, making him fall over the counter into a box of Donuts. Lars, Creeped out, Apologises, Steven and Jack then leave.
When Steven and Jack return to the temple, they are greeted by Amethyst who was thrown threw the warp pad, Garnet and Pearl run threw and look at a shadow coming out. Amethyst tells the two kids that they found the Gem Monster Creator: Onyx, the evil black gem, similar to the Grim Reaper. There is an earthquake and the Temple starts cracking, Onyx comes threw the warp and attacks Steven, who trues to summon his shield but fails, Garnet tells Amethyst and Pearl to fuse into Opal to defend Steven and Jack. After they fuse, theysummon their bow and arrow, they fend off Onyx, who runs into the Shadows
Garnet is waiting for Jack and Steven at the Warp pad, She needed to bring them to the Magma Spire, When they arrive, She tells them to Fuse into the Mega Powerful: Jade. Jack backs away and says he doesn't want to be a girl, Garnet gets angry and says its a guy, she teaches them to fuse, after fusing, Jade summons his Weapon, well, Half of it, Only Steven's Shield was summoned, Garnet forgets that Jack hasn't learned how to summon his Weapon, she askes them to defuse and Fuse with Steven to form Ruby Quartz, but Jade Disagrees.
jade goes on a rampage, at the Temple Garnet tells the Gems that Jade has been Formed and that Steven and Jack are in danger, they go to the Spire and see Jade destroying the Spire, Pearl and Garnet Form into Ruby, They start fighting, in the end, Onyx appears to take Steven, Onyx manages to seperate the two and takes both to his castle in the shadows,
Ruby and Amethyst Fuse into Jasper and she goes after Onyx, Steven summons his shield and hits Onyx in the head, he runs out of the Castle to see Jasper standing there, they look into the castle and see Onyx transforming Jack, Lion jumps into the Castle and rescues Jack, they return to the Temple and try to Summon Jack's Battleaxe.