“ Throw in a handful of random customs - like women or men of a certain level of society being required to wear a veil or a pendant of some type.”
“ A modern kingdom still strictly adheres to ancient traditions due to their long forgotten deity getting annoyed at the moral decay, appearing as an AI Singularity and forcefully correcting everything it sees as morally wrong. As such, even though the weapons and technology have improved, the culture hasn't.”
“ In the province of Behar in India, there is a bizarre custom that persists to the present day. Young men are kidnapped at knife (gun) point, and forced into marriage. If they refuse or cause trouble upon meeting their blushing bride-to-be, they are told that their family members will come to harm or even be killed if they resist. Some manage to fall in love or accept their fate. This scenario can be adapted to any rpg, ideally with a pc in the role of the abducted future husband!”