Is this a rare name..........................…

Question:

Yoko Manai .

Answer:

"Yoko" is a very common name.
洋子
陽子
遥子
and many others.

"Manai" is not very common, but there are some people whose surname is "Manai."
間内
真名井
真井
真那井
真内

I don't think it's so rare.