Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:6/8
K:Amin
['', 'GGA c2 e dcA', 'aba gag']  
X:1
L:1/8
M:6/8
K:Amin
 c |: GGA c2 e | dcA c2 A | GGA c2 e | dcA A2 G | GGA c2 e | dcA c2 d | eaa ged | ecA A2 G :| 
 aba gag | fed ecA | aba gag | ede g3 | aba gag | fed ecA | eee ede | cAA A3 :|  