this is the part where Rubia gets experimented on, most likely she becomes succubus through this. She was suspected of consorting w demons. They're going to do demonic testing on her and accidentally maker her the succubus.
Remember, when he says his master its to refer to his father. His view of the world is also skewed by his father being a sovereign (probably). The old man sweeping may have also been a sovereign and is giving Noh a nostalgia of sorts.