Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
Q:1/8=160
M:6/8
K:G
['AGA Bcd gdB', 'gfg efg']  
X:1
L:1/8
Q:1/8=160
M:6/8
K:G
 G3 AGA | Bcd gdB | GAB cBA | BGE GED |"^5" G2 G AGA | Bcd gdB | c2 A BdB | AGF G2 D | 
"^9" G2 B AGA | Bcd gdB | GAB cBA | BGE GDE |"^13" G2 G AGA | Bcd gdB | c2 A BdB | AGG GBd || 
"^17" g3 efg | a2 g fed | gfg efg | a2 a def |"^21" gfg agf | gfe fdB | c2 A BdB | AGG GBd | 
"^25" gfg efg | eag fed | gfg efg | a2 a def |"^29" gfg a2 a | g2 e fdB | c2 A BdB | 
 AGF !fermata!G3 |]  