Develop a musical piece incorporating the designated alphabet-based pattern and the supplied melodic theme.
X:1
L:1/8
M:6/8
K:Bmin
['fBB F3 f3 a3', 'd3 BFF D3 Bdf']  
X:1
L:1/8
M:6/8
K:Bmin
 fBB F3 | f3 a3 | fed cAA | E3 afe | fBB F3 | f3 a3 | g3 f2 e | dBA B3 :: d3 BFF | D3 Bdf | 
 ecB AEE | C3 ABc | d3 BFF | D3 Bdf | e3 fec | dBA B3 :|  