David Lerman wrote:

In several stories, Nodoka has suggested that Ranma marry Akane but have
Ukyou as a mistress and claims that this is a fine old Japanese custom.

Two questions: 1) Is the mistress an accepted Japanese custom regarded as
tradition?

In the past it was common place that a noble man be married through an
arranged marriage to have mistresses. The wife was seen as someone to
have sex with and to countinue the family line, feelings have little to
do with the relationship. The mistress took more of the role of a
personal companion and love of the man.

There were times in Japanese law the mistress had almost as much or even
the same rights as the man's wife in terms of inheiritence, ect...

It has only been since after World War II that having a mistress was
actually frowned upon by Japanese laws (because of U.S. influence). And
is probobly no longer an acceptable practice.

U.S. influence also has arranged marriages aren't that acceptible
anymore, but that didn't stop anyone from Ranma 1/2. 

With the Saotomes and the Tendos being 'traditional' families, Nodoka
suggesting Ranma taking mistresses is rather likely.

               2) If so, why doesn't Kuno consider the idea?  Then his only
decision would be the choice of which to marry.

He can't decide who to marry. He must wed them both!

                                                    dml