Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/16
M:2/4
K:D
['AG FDAF dAfa gfed cBAG FAdf gefd', 'f2d2d2 (3gfg afdA FAdf gfed cdeg fdba']  
X:1
L:1/16
M:2/4
K:D
 AG | FDAF dAfa | gfed cBAG | FAdf gefd | ecdB AFGE | FDAF dfaf | gfec dcBA | dfeg faeg | f2d2d2 :| 
 (3gfg | afdA FAdf | gfed cdeg | fdba gfed | cdef ecAG | FAdf bagf | edcB AGFE | FAdf ebag | 
 f2d2d2 :|  