Steven Universe focuses on the titular main protagonist, Steven Universe, the half-Gem, half-human hybrid boy who lives with the Crystal Gems, a small faction of female polymorphic sentient gemstones who resists the oppressiveness of the Gems' Homeworld. The cast consists of predominantly female characters (such as Garnet, Amethyst, Pearl, Connie Maheswaran, etc.) and naturally and unnaturally giant women (such as the Diamonds, and the giant Gem Fusions).
(A/N: The routes can include AU routes where the Gems are humanized.)
The only question is, which of these scenarios will you apply to the young Steven Universe male cast?
Size-Alteration: There are many ways that the Crystal Gems can shrink or grow. In one scenario, Steven tries to shapeshift with his Gem, but he ends up permanently shrinking with every failed try. In another scenario, a young male character around the required age limit or lower gets ahold of Homeworld's technology, leaving them shrunken and at the mercy of the giant women from Earth or Homeworld. In another scenario, Yellow Diamond demonstrates her size-alteration ability and uses it against the young humans of the Earth or the Zoo.
Born Tiny: The male cast is only a tiny fraction of the billions of children born tiny due to the genetic deficiency of the XY chromosome, so with a cast of predominantly female characters, they are doted on by the giant girls in their lives, or they are seduced by them. The characters are aware of the dangers posed to their sizes, so basically, it’s like any other episode of Steven Universe, but with a cast of bigger female characters.
Normal-Size Among Giantesses: The male characters are born normal-sized, but the female characters in the series are more massive than him. In one scenario, the Gems are all gigantic thanks to Yellow Diamond's size-alteration abilities to use for conquest, but the Crystal Gems are big enough to stop the conquest. In another scenario, the Gem Fusions are natural Gem giants who don’t need to be formed by fusing their base Gems (i.e. Sugilite, Sardonyx, Opal, Obsidian, etc.). In another scenario, a young male character is raised by the Diamonds, and they all indulge on his tiny size.
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Borrowers: The male characters are borrowers, a race of tiny people who hide within the walls of the bigfolk and "borrow" discarded or lost items. The borrower makes refuge in the home or a different location where a female character(s) from the series is prominently seen. (A/N: In this route, if Steven is born a borrower, then the Gems become humanized characters since Steven being born a half-Gem hybrid would tie in to the Born Tiny route.)