Short answers, pulled from the story.
The term blue blood originated from a social performance of warfare and lineage during the Reconquista. Noble warriors displayed blue veins beneath their pale skin to prove their untainted aristocratic birth against the dark-skinned Moorish enemy.
The nobility originated as a class of mounted warriors who swore allegiance to their sovereign in exchange for land and serfs. This system created a reciprocal relationship where nobles provided military service and protection in return for a fief, often land or office.
The hereditary nobility entitled to special rights has largely been abolished in the Western World since the end of World War I. By the 21st century, these titles were discredited as inferior to individual meritocracy in the allocation of societal resources.
The Ethiopian nobility were divided into Mesafint, the hereditary nobility forming the upper echelon, and Mekwanin, appointed nobles often of humble birth. The highest royal title after emperor was Negus, held by hereditary governors of provinces such as Begemder, Shewa, Gojjam, and Wollo.
The principalía was a unique class of nobility known as datus who retained governance of their territories despite annexation to the Spanish Empire. King Philip II of Spain ordered that these indigenous rulers continue to receive the same honors and privileges accorded them prior their conversion to Catholicism.
Following the Meiji Restoration in 1868, feudal titles and ranks were reorganized into the kazoku, a five-rank peerage system after the British example. This system ended in 1947 following Japan's defeat in World War II.