"Norinao" is real, or at least based on a "real person". It's just that I think his role and identity is completely changed here.
In history this person's name is actually Chigachi Noritada åč³å°åē“. This is an interesting case because normally ē“ in a name would be read as "nao", but in this case, all the sources I can find says that it's meant to be read as "Noritada".
He was possibly Hanzo Masanari's cousin.
The story of how this works is muddled with legends and folklore, but the best narrative that I could find was that at one point the Hattori family settled in a place called Chigachi in Iga. In that time they adopted the place name as their surname.
Through some chance, Masanari's father Yasunaga managed to gain employment with Ieyasu's family, and for this they reverted their name back to Hattori. As far as I could find, this happened during the time of Ieyasu's father or grandfather, which means it was back when their names were still Matsudaira. Masanari was not newly hired by Ieyasu, he was a generational vassal that was already there for many years.
Incidentally, Hattori Hanzo Yasunaga was Hanzo the First. While "Hattori Hanzo" usually makes people think of Masanari, he was actually Hanzo Junior/Hanzo the Second.
I think the trope of "there's a bunch of Hanzos everywhere in the Hattori clan" was popularised by manga/anime or dramas, but this was not the case in reality. Only Yasunaga's descendants have the name "Hanzo".
Yasunaga's brother Yasumoto, who remained in Iga, took over the leadership there in the Chigachi area (the extent of their domain/authority is unclear) and kept his name as Chigachi. Noritada is Yasumoto's son, and thus making him Masanari's cousin.
The reason why this is muddled is because some articles said that the Chigachi family is not related to the Hattori at all. The claim was that Yasumoto did have a brother named Yasunaga, but he isn't the same person as Hattori Yasunaga.
There are indeed many people with same names, and in the case of lords of smaller territories like this it's very easy to confuse one person for another.
Game spoiler of sorts:
