Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
M:4/4
K:D
['', 'd2 d2', 'A2 A2']  
X:1
L:1/8
M:4/4
K:D
 A2 |: dAFA GBAG | FAFA GBAG | FDFD GEGE | FDFD E2 c2 | dAFA GBAG | FAFA GBAG | FAdf g2 ec |1 
 d2 d2 d2 A2 :|2 d2 d2 d2 f2 |: ecAc efge | fdAd fgaf | ecAc efgf | edcB A2 A2 | BGGG BcdB | 
 AGFG A2 A2 | BcdB AGFE |1 D2 d2 d2 f2 :|  