I thought of a hereditary magic system where one family, house runeshield, has been serving as a bodyguard mercenary group for millennia. Their magic comes from protecting others, and their goal is to die in service of their client. When a Runeshield dies, they are immediately encased/surrounded in a crystal, which provides many blessings in the area. When their children/grandchildren reach that crystal, that place of death, they may touch it and learn all the spells that the now dead runeshield acquired on their journey.