Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
M:2/4
K:Emix
['g>f ef de', 'ef gf ec d>e fa ga', 'fd B>c']  
X:1
L:1/8
M:2/4
K:Emix
|: g>f ef | de B2 | g>f ea | ge be | g>f ef | de B2 | g>f ef | de e2 ::[K:Emin] c>d ef | gf ec | 
 d>e fa | ga fd | c>d ef | gf ec | d>e fa | ga e2 ::[K:Edor] e>f ge- | e/f/g fd | B>c dB- | 
[M:3/4] B/c/d ef ga |[M:2/4] e>f ge- | e/f/g fd | B>c dB | cd e2 :|  