Brief
A message was encrypted by XOR-ing it against a short word, repeated end to end for as long as the message lasted. All you get is the result, as hex.
The key is a single lowercase English word. Recover the message and read the flag out of it.
Hint
XOR is its own inverse, so plaintext ^ key = ciphertext also means
ciphertext ^ key = plaintext. You don’t know the key — but you do know what
English looks like, and every tenth byte was encrypted with the same one.