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
['D/E/F/G/ AF', 'fddf Afde']  
X:1
L:1/8
M:2/2
K:D
 B | D>FAF BGAF | D>FAF (d2 d)f | DFAF BGAF | E=ccE (G2 G)B | D/E/F/G/ AF BGAF | 
 D/E/F/G/ AF (d2 d)f | D/E/F/G/ AF BGAF | E=ccE (G2 G) || g | fddf Afde | fddf (a2 a)b | 
 fddf Afde | =cdef g3 b | fddf Afdg | fddf a3 b | afge fdec | E=ccE G2 G ||  