Craft a musical piece in accordance with the designated structure and theme.
X:1
L:1/8
Q:3/8=120
M:6/8
K:Bb
['B2 B', 'B3 B2 B f2 f b>ag f3'  
X:1
L:1/8
Q:3/8=120
M:6/8
K:Bb
 B2 B f2 f | d>cd B3 | B2 B c2 d | e2 f d>cB | B2 B f2 f | d>cd B3 | B2 B c2 d | e2 f B3 :: 
 B2 B f2 f | b>ag f3 | F2 F e2 e | gfe d3 | E2 E c2 c | e>dc B2 b | B2 g f>ed | c>BA B3 :|  