Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
Q:1/8=160
M:6/8
K:D
['FED EFG Adf ecA', 'f3 d2 B Adf agf']  
X:1
L:1/8
Q:1/8=160
M:6/8
K:D
 F3 G3 | FED EFG | Adf ecA | G3 EFG | FAd GAd | FED EFG | Adf ecA | GEA D3 :| f3 d2 B | Adf agf | 
 e2 f gfe | efd cBA | f3 d2 B | Adf agf | Bef gab | aec d3 :|  