As part of the cultural gulf between the US and Japan -- something that is topical for today's Women's FIFA World Cup final between the US and Japan -- I present the following clip about what baby names Rosie Pope likes and dislikes:
Now, I know that Rosie Pope probably isn't an American (her accent sounds British), but the point is that when it came to using numbers as names, both she and the interviewer were negative to the idea of using numbers as a name (indeed, the interviewer didn't even know that people did this). While I don't know how common the practice is anymore in Japan, the use of a number in the name was not uncommon historically. Indeed, the high school principal of my school in Tokyo had the given name "Saburo" (三郎), which literally means "third son." Also, the name "Ichizō" (一三) literally means "one three": a number (and also the name of one of my uncles).
Okay, okay, okay, the naming conventions of Japan shouldn't be at the forefront of white Americans (and Brits), but in a world where Americans are naming their children after fruit (like Apple), natural features (James Mountain Inhofe), etc., the idea that someone might name their child after a number -- even in English -- shouldn't be too surprising.