Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
Q:1/4=100
M:6/8
K:G
['G>AG A2 d', 'G4 e/f/ gfg efg aga fed gfg']  
X:1
L:1/8
Q:1/4=100
M:6/8
K:G
 D | G>AG A2 d | B G2 z2 d | gfg eag | f d2 z2 f | gfe dcB | ABG FED | G>AG A2 d | B G4 :: e/f/ | 
 gfg efg | aga fed | gfg eag | f d4 e/f/ | gfe dcB | ABG FED | G>AG A2 d | B G4 :|  