Unfortunately Angry Birds has not yet become popular in Japan. It gradually spreads among Japanese players, but has not yet led to a big hit. Therefore Rovio Japan started original development only in Japan for the Japanese players acquisition in Angry Birds Epic.
At first they opened an official site of Angry Birds Epic of the Japanese version. The summaries of Angry Birds Epic are explained in Japanese in detail here. Japanese is natural, and there are not mistakes and the unnaturalness that overseas games have.
Furthermore, they appeal to Japanese players to pre-registration here. Special item "Ronin" is presented to players who pre-registered. This is general technique in the Japanese mobile/social game industry. Now, it is not unusual for tens of thousands of players to gather at a stage of the pre-registration.
According to the email from Rovio Japan staff, they carry out a pre-registration event only for Japan to have more players play Angry Birds Epic in Japan which is the main market of the RPG. Special item "Ronin" is the upgrading item which is available for the main character Red, and The designer of head office in Finland imagined samurai and designed it. It is Kabuto(兜: helmet of Japanese armor) definitely.
By the way, "Ronin"(浪人) means a samurai with no lord or master in Japanese. And, it means the people who fails the exam now :D
I think Kabuto for simple is better.