What hides between Shadow and Light?

[Villane]

Some thoughts: you could take only the letters from the alphabet that are fibonacci numbers
1 A
2 B
3 C
5 E
8 H
13 M
21 U

The transformations (results are also fibonacci numbers):

20 T -> B 2 ( 2+0 = 2 )
3 C -> C 3 ( 3=3 )
17 Q -> H 8 (1+7 = 8)