Tangent
Space exists but only up ( the world is an infinite crystalline plane, down is always in and up is always out )
Magic exists
Magic is dangerous in space
Mages are a highly managed caste, often to the level of oppression, slavery, and eugenics
Some rogue mages exist but only on authority from the Concordat
Concordat is a general peace agreement between a land as diverse as Mass Effect and as spread out as in firefly or serenity
"Casting Tangents" is space travel, Tangent Runners or Tangent Ships are specialized vessels that have the ability to navigate the ever shifting crystalline plane.
They do this through the power of mages known as Speakers.
Through magic, Speakers turn themselves into tangent ships, allowing them a vast array of higher powers.
Tangent ships can be as big as a castle (multiple speakers banding together into one massive vessel)
Or as small as a shuttle, though these are more rare.
Tangent Running is not Perfect, and Speakers do not last forever. Speakers live longer than most, but deteriorate after a while. Larger vessels like Floating Castles are often operated bu pseudo-religious sects through spiritually devoted sacrifice (or slaves)