Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
Q:1/8=300
M:6/8
K:D
['B>cd efg (fb)g f2 d/e/', 'd3- dfA']  
X:1
L:1/8
Q:1/8=300
M:6/8
K:D
|: F | B>cd efg | (fb)g f2 d/e/ | (fa)f ede | fdB cAF | B>cd efg | (fb)g f2 d/e/ | faf edc | 
 B2 z z2 :: z |{g} a6 |{a} bza fde |{d} f6 |{f} azf eAB | d3- dfA | d3- dfA | (df)A (df)A | 
 def gab | a6 |{a} bzg fde |{d} f6 |{f} azf dAB | d3- dfA | d3- dfA | (df)A (df)A | d2 z z2 :|  