Craft a piece of music that integrates both the suggested theme and letter-based structure.
X:1
L:1/8
M:4/4
K:D
['FG ABAF A2 de fgef d3 A', 'ag fefg afdf edcB A2 ef ggag']  
X:1
L:1/8
M:4/4
K:D
"^A" FG | ABAF A2 de | fgef d3 A | BcdB ABAF | G2 E2 E2 FG | ABAF A2 de | fgef d3 A | BcdB ABAG | 
 F2 D2 D2 :|"^B" ag | fefg afdf | edcB A2 ef | ggag ffaf | g2 e2 e2 FG | ABAF A2 de | fgef d3 A | 
 BcdB ABAG | F2 D2 D2 :|  