Well, I don't know too much about US laws, but even if there was some law, it should be really easy to get around it. A company could just use a daughter company in some other country where no law forbids buying foreign companies. Most big companies, like Microsoft, already have such subsidiaries in multiple countries to bypass optimize tax payments. 

With american companies buying foreign companies all the time, I really don't see any problem here. A quick google search showed me no laws whatsoever from japan that would possible come in the way, even buying solely with stocks is possible. It's also certainly possible the other way around, as seen last year when a japanese company bought the makers of Jim Beam. 

I think it'd be great if Microsoft bought Nintendo: would mean Nintendo games might eventually show up on PC.

Highly doubt it's ever happening though.

Them two would still get their ass kicked.

Nin MS would be one voilatile envirement where majory of the devs would leave after a year.  Two stubborn arrogant parties with two different minded nationalities budding heads.  It would be fun to see.

Stop the presses! No way.

I'm sure nobody would mind having more games for their system :p

If NX fails like the WiiU has so far, I have a feeling that Nintendo may get out of the hardware market and become a 3rd party publisher. Never thought I'd say this but it may be a more profitable business for them given the number of franchises they have and own.

Who in their right mind WOULD mind Nintendo games on their platforms?

Lol, of course he wouldn't. Who would really?