Is your character human? Yes and no. I don't really think Primo counts as a human anymore, he doesn't consider himself human and he certainly doesn't exist as one either even if he appears in human form. I don't remember right now if it's ever stated how Shinigami Eyes work on Shinigami, but however they work on them it should be how they work on Primo.
Any abnormalities that could be picked up by the eyes? As I said I don't remember if a human with the eyes can see a Shinigami's name or lifesan, in case they can see either or both of them: I headcanon that Primo's name is hard to read as if two names are written one on top of the other, with patience one could make out the names of Keiichi Maebara and Primo (it's not a nickname case as both are his name, it's just that Keiichi is a name he hasn't used in thousands of years). About the lifespan it would be crazy high, so high it doesn't seem to decrease, as he's a literally eternal existence.
I hope this made sense and serves for something ^^'UU
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Is your character human? Yes and no. I don't really think Primo counts as a human anymore, he doesn't consider himself human and he certainly doesn't exist as one either even if he appears in human form. I don't remember right now if it's ever stated how Shinigami Eyes work on Shinigami, but however they work on them it should be how they work on Primo.
Any abnormalities that could be picked up by the eyes? As I said I don't remember if a human with the eyes can see a Shinigami's name or lifesan, in case they can see either or both of them: I headcanon that Primo's name is hard to read as if two names are written one on top of the other, with patience one could make out the names of Keiichi Maebara and Primo (it's not a nickname case as both are his name, it's just that Keiichi is a name he hasn't used in thousands of years). About the lifespan it would be crazy high, so high it doesn't seem to decrease, as he's a literally eternal existence.
I hope this made sense and serves for something ^^'UU