Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:4/4
K:Bmin
['B2 FB- BFBd c2 ec', 'f2 df- fBdf']  
X:1
L:1/8
M:4/4
K:Bmin
|: F2 | B2 FB- BFBd | c2 ec dcBA | B2 F B2 A2 G- | G F2 E2 F3 | B2 FB- BFBd | c2 ec dcBf- | 
 f2 gf edcd | B2 B2 B2 :: d2 | f2 df- fBdf | ggag fede | f2 df- fBdf | edce dcBd | f2 df- fBdf | 
 ggag fedf- | f2 gf edcd | B2 B2 B2 :|  