is that a pun of a real sengoku era general?
Well, the first of the three Great Unifiers of Japan is Oda Nobu
naga, and since it took Toyotomi Hideyoshi and Tokugawa Ieyasu successively to complete the unification of Japan, it seems that Kanzaki Takenaga may be intended to represent a fusion of the three figures.
Either that, or those three still exist, it's just that Takenaga was the one who secretly ensured those three stayed on track in the quest for a united Japan, thus being historically obscure while the other three became famous.