Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
M:2/2
K:D
['FAAF GAAG FABc', 'afdf (3gfe fd']  
X:1
L:1/8
M:2/2
K:D
 DFDG FAAF | GAAG FABc | dBAG FADf | (3gfe fd ecAF | D2 DG FAAF | GAAG FABc | defd ecdB | 
 AFGE FD D2 :| faaf afdf | (3gfe fd edBc | d3 B AFDe | fedf e3 g | fa a2 afdf | (3gfe fd edBc | 
 defd ecdB | AFGE FD D2 | fa a2 afdf | (3gfe fd edef | g2 bg fgaf | gfed (3Bcd eg | f2 af bfaf | 
 gefd edBc | defd ecdB | AFGE FD D2 ||  