Regarding reservation at Hotel Nikko Kansai Airport. Japanese website says that reservation become available from around 45 days in advance for Nikko Hotels in Japan, depending on specific hotel. If I look up reservation for July 2014 then give a message that no room is available, just like you mentioned. Then went to rate calendar on the website and rate is shown up till end of March 2014 at this moment, anything further simply show “-“ as rate not available.
I went to JTB website (one of largest travel agency in Japan) and JTB website shows rate at Hotel Nikko Kansai Airport up till first week of May 2014 at this moment.