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 eBB cBc A2 B cff', "c'2 b"]  
X:1
L:1/8
M:6/8
K:Bmin
 B2 g |: fBB eBB | cBc A2 B | cff cff | ecB Afe | fBB eBB | cBc A2 B | cff ecA | (B3 B) z2 :| 
 bc'b baf | bab c'2 b | aba afe | fef a z2 | c'ac' baf | b3 c'2 b | aff ecA | B3 B z2 :|  