User blog comment:Hitsuji Mamoru/Servant Creation Room 2 : Guess of the Who/@comment-4802891-20170727204532/@comment-4802891-20170811063036

You are close. He is indeed a political decoy, but not Takeda Shingen's. Since you are pretty close I'll give you this : he has been the decoy for so long that he is, historically (for some conspirationists, and an aspect of the Nasuverse), remembered as the real person. The ghost haunting him in life, was this person.

Find the name of this person, and you have it.