Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
M:3/4
K:D
['Af db Af', 'b>g ^c2 e2', '(df) (fa)']  
X:1
L:1/8
M:3/4
K:D
"D" f>e d2 !>!B2 | !>!A4 A2 | f>e d2"^(G)" !>!B2 |"D" !>!A4 A2 |"A7" c>d e2 !>!b2 | !>!a4 a2 | 
 c'>b a>g Bc |"D" !>!d4 A2 |:"D" Af db !>!a2 | Af db !>!a2 | Af d2 b2 |"A7" !>!a4 A2 | 
 Ae cb !>!a2 | Ae cb !>!a2 | A>B c>d e>f |1"D" d4 A2 :|2"D7" d4 b>g ||[K:G]"G" !>!d2 ^c2 e2 | 
 !>!d4 b>g | !>!d2 ^c2 e2 | !>!d4 f>g |"D7" a2 f2 e2 | !>!d4 d2 |"G" !>!d2 b z a2 | g4 d2 |: 
"G" (dg) (gb) !>!b2 | (dg) (gb) !>!b2 |"C" c'>b a2 g2 |"D7" !>!f4 d2 | (df) (fa) !>!a2 | 
 (df) (fa) !>!a2 | a>g f>e d>d |1"G" !>!g4 b>g :|2"G" g4 z2 |]  