Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:3/4
K:D
['f>e d2 d2 d>f e2 e2', 'f>g a2 a2']  
X:1
L:1/8
M:3/4
K:D
|: f>e | d2 d2 d>f | e2 e2 e>g | f2 ba gf | e4 f>e | d2 d2 d>f | e2 e2 ba | ab af ef | d4 :: f>g | 
 a2 a2 ba | a4 f>g | a2 a2 bf | e4 f>e | d2 d2 af | e2 e2 g>b | ab af ef | d4 :|  