Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
M:6/8
K:D
['FEF D2 d cAG F2', 'D2 d']  
X:1
L:1/8
M:6/8
K:D
 FEF D2 d cAG | F2 D AGF GFE | FEF D2 d cAG | F2 A G2 B AFE | FEF D2 d cAG | F2 D AGF GFE | 
 FEF D2 d cAG | F2 A G2 B AFE || D2 d cAd cAG | F2 d A2 F GFE | D2 d cAc ded | F2 A G2 B AFE | 
 D2 d cAd cAG | F2 d A2 F GFE | D2 d cAd fed | F2 A G2 B AFE ||  