Ryouga is an only child. In the story where Ryouga's dog Shirokiro
(horribly translated by Viz as Checkers!! in the most recent issue) has

That's not a translation, that's a Reagan joke.

Actually, it's a Nixon joke. (You were close, they were both late 20th
century Republican presidents, though Nixon was Ike's VP at the time that
he made the "Checkers Speech"). One assumes that someone at Viz is a Nixon
fan. ;)

Well, I went and asked about this 'Checkers' thing because I didn't find
it funny, so I wanted to know if it was an 'in joke' (for Americans)...

Here's the answer I got:

I didn't choose it, but it makes sense. Shirokuro means black-white, so
it's the beginning of a check pattern, thus Checkers.

[snip question about some president guy's dog]

It's nothing so convoluted as that.

Kun-chan ...