Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:6/8
K:G
['|1,3 DFA', 'B c2 d B2 G :|2,4 DFA']  
X:1
L:1/8
M:6/8
K:G
|:"^Sequence A4 B4""^A" DGB DGB | BAG A2 F |1,3 DFA DFA | cBA B2 G :|2,4 DFA cBA | DEF G3 |: 
"^B" DGB d2 ^c | d2 c A3 |1,3 DFA c2 B | c2 d B2 G :|2,4 DFA cBA | DEF G3 ||  