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
['dB AF F2 G2 FG ADFD EGFE', 'f3 e defe dBAF']  
X:1
L:1/8
M:4/4
K:D
 dB | AF F2 G2 FG | ADFD EGFE | D2 FA defe | dBAF E2 dB | AF F2 G2 FG | ADFD EGFE | D2 FA defe | 
 dBAF D2 :| de | f2 fa g2 fg | afdf edBe | f3 e defe | dBAF E2 fg | af f2 bf f2 | afdf efde | 
 f3 e defe | dBAF D2 :|  