Osaka Tokyo Osaka in Obon

We're flying to Kansai Intl on August 8 arriving 7:55pm and departing on August 16 at 8:40pm.
Our plan is to go straight to the Willer bus terminal in Umeda and take the overnight bus to Tokyo Disney Sea but their rates are \7600 up already. Will the rates go down?
We plan to stay in Tokyo for a few days and go back to Osaka for the remaining few days, what date is best for us to head back to Osaka to avoid the travel rush?
Would it be cheaper to fly Peach air than Willer bus?
Thanks to everyone who will give their advise.
Cheers!

As a follow up, during Obon, The main city dwellers like Tokyo and Osaka go out so does that mean they're quieter?

As a follow up, during Obon, The main city dwellers like Tokyo and Osaka go out so does that mean they're quieter?

It is not always true in every major city. In a traditional sense of Obon like that a family commemorates ancestors, there may well be many families who travel to a major city in order to visit their ancestors�f grave. In another sense of Obon like that recitatives or acquaintances living apart meet together, there may well be many people who choose to visit popular spots in major cities.

The meaning of Obon and dates of Obon holidays may differ by persons or families. Dates of Obon and Obon-related events vary by areas.
Generally speaking, the 13th and the 16th of August and one or two weekends around the two days are expected to be busy with many long-distance travelers. That is tendency concerning only the beginning and the ending of the Obon movement. It is not easy to predict when and how will which tourist spots be crowded with Obon travelers.
http://www.japan-guide.com/e/e2286.html

Thanks Omotenashi.