Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:4/4
K:G
['D (G3 A) (cBAG) B2 d2 g2', 'f2 e2']  
X:1
L:1/8
M:4/4
K:G
 D | (G3 A) (cBAG) | B2 d2 g2 (fg) | e2 d2 (Bcd>B) | A4 G2 z :| d | g2 f2 e2 (fg) | f2 e2 d3 ^d | 
 e3 B B2 ^d2 | (e3/2f/4e/4d/4e/f/) !fermata!g3 g | (G3 A) (cBAG) | B2 d2 g2 (fg) | e2 d2 (Bcd>B) | 
 A4 G2 z ||  