Complex sentence: It was the first P MODEL album to feature band-leader (Susumu Hirasawa) as the only remaining founding member of the group, due to (Sadatoshi Tainaka), the original drummer, leaving to live on (Galápagos Islands).
Split into simpler sentences: It was the first P MODEL album to feature band-leader (Susumu Hirasawa) as the only remaining founding member of the group. Hirasawa was left as the only remaining founding memeber after (Sadatoshi Tainaka), the original drummer, left the band to live on (Galápagos Islands).