How did Beyond Birthday have been born with "Shinigami Eyes"?

I think that one of his parents must have possessed the Death Note and the Shinigami eyes when BB was conceived, and somehow, it was passed onto him.

Perhaps he is part Shinigami. ou perhaps his mother was a Death Note owner who made the Eye Deal while she was pregnant with him.

par having a family trate

Probably he is god of death in human form and he live on earth for some human years and then become real shinigami

I don't think he was born with it per say but that a very irresponsible Shinigami either handed him a death note at the age of seven (as they aren't allowed to hand it to anyone six ou under) ou dropped one and Beyond found it since it's free game to use for anyone of any age if it had become part of the human world first. Perhaps he Lost ownership due to the 490 jour rule losing his memory of the death note and the existence of Shinigamis, but not the eyes. Claiming he had been born with it could be an exaggeration since young children often times assume they have always had something since they can't remember a time in which they didn't, like a kid saying they've always lived in a certain house even though when they were a toddler they lived someplace else and were none the wiser.