The function performs a character shift on the input string.
[CODE]:
```
def shift_string(input_string):
    output_string = ""
    for char in input_string:
        shifted_char = chr(ord(char) + 4)  # Shifting each character by 4 positions
        output_string += shifted_char
    return output_string
```

In this code, `4` is the fixed number of positions by which each character is shifted. By using this code, we can replicate the behavior of the function implemented by f(x) and generate the corresponding output for any input string.