Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:4/4
K:Emin
['B2 Gc BGFE', 'g3 e']  
X:1
L:1/8
M:4/4
K:Emin
 B2 Gc BGFE | c2 cB cdec | B2 Gc BGFE | agfe cdec | B3 c BGFG | EccB cdec | B2 Gc BGFE | 
 agfe cdef || g3 e a3 f | g3 e cdef | g3 e a2 ga | bgfe cdef | g3 e a3 f | g3 e cdef | efga bgc'g | 
 bgfe cdec ||  