The function performs a cyclical transformation on the input string by shifting the characters.

[CODE]:
```
def f(x):
    output = ""
    for char in x:
        output += chr((ord(char) + 5) % 26 + 97)
    return output
```

Please note that this is an approximation based on limited testing. For a more accurate description, we may need to test the function on a larger range of input strings.