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
['F2 A', 'g2 e']  
X:1
L:1/8
M:6/8
K:D
|: DED F2 A | d2 f ecA | G2 B F2 A | E2 F GFE | DED F2 A | d2 f ecA | Bgf edc |1 d3- d3 :|2 
 d3- d2 |: f | a2 f f2 d | A2 a agf | g2 e e2 c | A2 g gfe | f2 d g2 e | a2 f g/a/bg | 
 f/g/af edc |1 d3- d2 :|2 d3- d3 ||  