Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:6/8
K:D
['d2 d c2 A BdB AGF G2', 'd2 f a2 b afd a2 f']  
X:1
L:1/8
M:6/8
K:D
|: A | d2 d c2 A | BdB AGF | G2 e F2 d | E2 d cBc | d2 d c2 A | BdB AGF | G2 e F2 d | cBc d2 :: A | 
 d2 f a2 b | afd a2 f | A2 c e2 f | ecA e2 c | d2 f a2 b | afd a2 f | gbg faf | edc d2 :|  