Jolf, 17 bytes
pq#-w^88C Li1~560
pq pad
_Li1 the input, w/out the first char
C ~5 parsed as a base-16 integer (~5 = 16)
w^88 8 ^ 8 - 1 (the magic number)
- subtract the parsed input from said number
# convert result to hexadecimal
60 pad the result with 6 0's
Try it here!, Test suite (Use full run, which now works.)