Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:4/4
K:D
['f>g a>f', 'g>e B<d']  
X:1
L:1/8
M:4/4
K:D
"A" | B |"D" A2 A>B A>B d>e |"D" f>A"A" e>A"D" f>d"G" B<d |"D" A2 A>B A>B d>e | 
"D" f>d a>f"A" e2"D" d :|"B" | e |"D" f>e d>e f>g a>f |"A" e>d B<d e>f g>e |"D" f>e d>e f>g a>f | 
"Em" g>e"D" a>f"A" e2 d || e |"D" f>e d>e"Bm" f>g a>f |"Em" e>d B<d"A" e>f g>e | 
"D" f>a"A" e>f"D" d>f"Bm" B<d |"D" A>d"D" a>f"A" e2"D" d |]  