The answer to the question: What role did marriage play in the feudal systems of both Europe and Japan, would be, B: Marriage tightened alliances between noble families.
Feudalism became a common feature of the ruling system both in all of the European continent, and also, funnily enough, in Japan. While in Europe feudalism was born in the 9th century as a result of the dissolution of the Carolingian Empire, in Japan, this happened from 1185 CE until 1868 CE, when, after a series of rebellions against the Japanese emperor, power was turned over to the Shogun, the Samurai and the daimyo. The first two, were the military power of the nation, while the third, were the noble families in the realm. In both cases, Europe and Japan, marriage was used as a means to strengthen power and alliances between the noble families, in order to gain lands, more riches, and also to ensure military power, which also ensured protection from those who wanted to acquire more power and lands through military strength.