Musashimaru to be a naturalized Japanese?

[Yugo Yodogawa <yyy@CSUA.Berkeley.EDU>]

> If Musashimaru wants to stay in Sumo community after his retirement, he
> needs to become a naturalized Japanese citizen and get a Toshiyori Meiseki.
> The average value of Toshiyori Meiseki is about a milion dollar. If he
> decide to stay in Sumo community, he needs to find a future "okamisan",
> probably a Japanese. Okaminan is like a mother to all young rikishi, and it
> is hard to imagine other than Japanese "okamisan".

Is it even possible to become a naturalized Japanese citizen without marrying
a Japanese person?  Musashimaru _must_ marry a Japanese woman in order to
become a citizen, right?