Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
Q:1/8=180
M:6/8
K:D
['ABA f2 d', 'aAa fed']  
X:1
L:1/8
Q:1/8=180
M:6/8
K:D
|: A | ABA f2 d | efa fed | ABA f2 d | edA B2 d | ABA f2 d | efa fed | efa f2 e | dBA A2 :: f | 
 aAa fed | aAa fed | aAa fed | f2 e e2 f | aAa fed | eAA f2 d | efa f2 e | dBA A2 :|  