Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
Q:1/2=90
M:4/4
K:C
['ABcA F2 fg agaf d2 cB AB', 'fgaf ge c2']  
X:1
L:1/8
Q:1/2=90
M:4/4
K:C
 C |[K:F] uedcB | ABcA F2 fg | agaf d2 cB | AB c2 dcBA | A2 G2 G2 cB | ABcA F2 fg | agaf d2 cB | 
 AB c2 agfe | f2 F2 F2 :: de | fgaf ge c2 | fgaf ge c2 | cABc dcBA | A2 G2 G2 cB | ABcA F2 fg | 
 agbf d2 cB | AB c2 agfe | f2 F2 F2 :|  