The weird thing about Casiopea is that, individually, every single member of the band was a fantastic instrumentalist and prone to experimentation. If I remember correctly, the drummer is generally thought to be one of the best in Japan and the bassist went on to release an album ("Solo Duet Trio" or something like that) consisting of songs entirely built out of multi-tracked bass lines run through synths. Legends like Kazumi Watanabe got involved in these side projects, etc. etc.
So you get all these awesomely odd jazz musicians, slap them together and they make... this.