The function reverses the input string and replaces each character with the 7th character that comes after it in the ASCII table.

[CODE]:
```python
def f(x):
    reversed_x = x[::-1]
    output = ''
    for char in reversed_x:
        output += chr(ord(char) + 7)
    return output
```

This code approximates the behavior of the function by reversing the input string and replacing each character with the 7th character that follows it in the ASCII table.