Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
Q:3/8=100
M:6/8
K:G
['bgg g2 b afd d2', 'D2 B/c/ dBc dge dcB c2 A/B/']  
X:1
L:1/8
Q:3/8=100
M:6/8
K:G
 g/a/ | bgg g2 b | afd d2 e/f/ | gfe dcB | ABc BAG | bgg g2 b | afd d2 g | fed Ad^c | d3 D2 :: 
 B/c/ | dBc dge | dcB c2 A/B/ | cAB cde | edc B3 | BGA Bcd | egf g2 c | BAG DGF | G3- G2 :|  