Bushiroad revealed the fifth extra booster set; Primary Melody. This booster set is exclusive for Bermuda Triangle. It also serves as an expansion for the upcoming Trial Deck Vol.08 Schokolade Melody. The package image features Sonata. However, Sonata’s skills have not been revealed at the moment.
I strongly recommend buying this Primary Melody if you are want to play Bermuda Triangles for the Standard format. You will be able to upgrade your trial deck with new cards. You also may be able to create a second deck with a different vanguard. None of the cards has been revealed. The new cards may be useful in the Premium format, but we must wait and see the cards.
Primary Melody is scheduled to be released on March 29th, 2019 in Japan, and the release for English is to be determined at a later date.