In Osaka (w/ Expense Acount!)
My favorite expense-account restaurant used to be Chunagon, a lobster (iseebi) paradise (I love lobster). Every course is lobster based--from lobster salad and sashimi to lobster soup and grilled lobster.
However, the last time I was there was more than 10 years ago and I'm not sure if the food is still good. So you may want to ask someone who has been there recently.
The company has been existence for 50+ years. It's headquartered in Nishinomiya (between Osaka and Kobe) and there are two locations in Osaka and two in Kobe. (I used to go to the one in Kita-Shinchi, but it closed before I knew.) They have private rooms.
This is the menu at Umeda location.
(I took a couple of American businessmen there 20 years ago and they loved the food.)
More expensive courses have "ikezukuri" (live sashimi).
Also, you should definitely try Kobe Beef while you're in Osaka/Kobe. My favorite place is in this thread, but it's reasonably priced so you might want to save it for your non-expense-account visit ;-) (Other people mentioned other options.)