Japanese character Riki stands for power, and Maru is specifically used
for a boat in Japan. Root of traditional Japanese drum (Taiko) is in a sea.
At the time when boat had no engine, people pulled an oar for moving a boat.
 In order to make safety and most efficient sailing, all of oar must be 
synchronized and used rhythm of Taiko for this purpose. Therefore people 
decided to have Japanese drums and players even they reduced one oarsman.
 There are many traditional entertainments, which make association between 
a Japanese drum and a boat, in Japan even inland area. Most popular one is 
in Chi-chi-bu, which is located in the north of Tokyo. 
It was called "Chi-chi-bu Yatai Bayashi". We used this as a motif of Riki-Maru, 
and liken Wadaio Matsuriza to one big boat to express a story of voyage.