We had stayed in Nikko Osaka before...very convenient just opposite 心齊橋. There is a subway kind of entrance directing to the JR station and the Japanese department store right under the / next to the hotel.
Thanks a lot, I have booked the Nikko Osaka online directly to the hotel, because I have tried many agents and can't made the reservation included Nikko Osaka, Hotel Riva, and New Osaka Hotel, so now I tried to booked directly from the hotel but I guess the rates must be much higher....