Design a musical composition incorporating the alphabetic expression of the chosen structure and the provided melodic theme.
X:1
L:1/8
Q:3/8=120
M:6/8
K:C
['G gag fed cde G2 g c2', 'd2 d efe']  
X:1
L:1/8
Q:3/8=120
M:6/8
K:C
 G | gag fed | cde G2 g | c2 c dcd | efe d2 G | gag fed | cde G2 g | c2 c dcd | [cC]4 :: G | 
 d2 d efe | d2 d efe | gag fgf | efe d2 G | d2 d efe | d2 d efe | g2 f edc | G2 B [cC]2 :|  