Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
Q:1/4=90
M:6/8
K:G
['B2 B']  
X:1
L:1/8
Q:1/4=90
M:6/8
K:G
 D | B2 B (dc) B | A2 A G2 G | c2 c d2 c | (B3 B2) G | B2 B B2 F | A2 A G2 B | A2 (dA) B ^c | 
 (d3 d2) D | d2 d (d2 A) d | d3 d2 =c | B2 B B2 A | (G3 G2) G | G2 E (DG) B | d2 d c2 B | 
 G2 G (DE) F | (G3 G2) |]  