Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
Q:3/8=90
M:6/8
K:Gmin
['B2 G AFD', 'fgf fcA']  
X:1
L:1/8
Q:3/8=90
M:6/8
K:Gmin
 B2 G AFD | B2 G AFD | F3 F2 A | F3 F2 A | B2 G AFD | B2 G AFD | G3 G2 B | G3 G2 :| A | Bcd cBA | 
 BAG AFD | fgf fcA | fgf fcA | Bcd cBA | BAG AFD | gag gdB | g>ag g2 A | Bcd cBA | BAG AFD | 
 fgf fcA | fgf fcA | Bcd cde | dcB AG^F | G3 G2 B | G3 G2 |]  