OK Music has a two page interview with Kiiyan and e-zuka here, discussing this week’s release, 『M・S COWBOYの逆襲』.
In the interview we learn that the idea for the concept album came from staff (and quite likely e-zuka’s drinking). e-zuka was apparently influenced by both Led Zeppelin for 「Imaginary song」. We also learn that many tears were shed during the recording (Kiiyan claims their “lacrimal glands” have weakened as they’ve aged. When asked what song recordings made them cry in the past, e-zuka says 「Happy Life」and Kiiyan says 「Under the Sky」 (I’m with Kiiyan on this one.)
The interviewer also points out this is the first album to have no anime tie-up. Kiiyan says that while that’s true, the 「delight song」single didn’t have any either, and that he hopes this concept album will be well-received, despite the lack of tie-up.