The function replaces certain characters in the input string ('d' with 'h', 'e' with 'l', 'f' with 'a', 'g' with 'i', 'p' with 'x', 'q' with 'y', 'r' with 'n' and vice versa), and then appends an 'i' at the end of the modified input string.

[CODE]:
```python
def f(x):
    replace_map = {'d': 'h', 'e': 'l', 'f': 'a', 'g': 'i', 'p': 'x', 'q': 'y', 'r': 'n',
                   'h': 'd', 'l': 'e', 'a': 'f', 'i': 'g', 'x': 'p', 'y': 'q', 'n': 'r'}
    result = ''.join([replace_map.get(char, char) for char in x])
    return result + 'i'
```