Rexin

Title given to the ruler of the Maistian kingdom or monarchy, it was the highest possible rank.
  This rank was a lifelong and hereditary one, passed down to the closest legitimate relative regardless of gender.
  The marital partner of the Rexin was not given any special title per se but they typically still enjoyed the benefits (not powers) of a royal status. If there were multiple partners, the Rexin was obligated to show no favoritism or a divorce could be issued.
  If a young child was crowned the monarch, then a regent was often appointed to govern until the monarch reached the requisite adult age to rule. This was the only case in which a person who had married into the royal family could, temporarily, enjoy the same power than if they were the ruler in their own right.
  Any potential legitimate heir to the title was referred as the Prosan, sometimes with a number if there were many children, such as 'Second Prosan.
  In the former Maistian kingdom's order of successions, the person closest in degree of kinship to the sovereign succeeded, preferring elder over younger siblings. The Rexin's partners were not elligible as they were not considered sharing the sovereign's blood. Therefore, regardless if the late ruler had descendants or not, their siblings would succeed them, then followed by the late ruler's children from eldest to youngest and finally their siblings' children in that same order. All of which was done regardless of gender.
  The term itself was gender neutral.
Real-Life Equivalent
Rex (title)
Meaning
Ruler
Etymology
'rex' king, ruler (lat) + 'in'
Type
Royalty, Hereditary
Status
No longer in official use since 341
Form of Address
His Majesty / Her Majesty ; then Sir / Ma'am
Current Holders