Develop a musical piece incorporating the designated alphabet-based pattern and the supplied melodic theme.
X:1
L:1/8
Q:3/8=110
M:6/8
K:D
['a aef', 'A Aeg bag g3 f2']  
X:1
L:1/8
Q:3/8=110
M:6/8
K:D
 a | aef d(fe) | A3 ABc | def gab | ^g3 a2 a | aef dfe | A3 ABc | dfb aef | d3 d2 :: A | Aeg bag | 
 g3 f2 f | fed dcB | BA^G A2 A | Aeg bag | g3 f2 d | d>cB BA^G | A3 a2 :|  