The function replaces the last character in the input string based on the following rules:
- Replace 'o' with 'x'
- Replace 'd' with 'm'
- Replace 't' with '}'
- Replace 'l' with 'u'
- Replace 'n' with 'w'
- Keep the last character unchanged in other cases

[CODE]: 
```python
def modify_last_char(s):
    last_char = s[-1]
    replacements = {
        'o': 'x',
        'd': 'm',
        't': '}',
        'l': 'u',
        'n': 'w'
    }
    new_last_char = replacements.get(last_char, last_char)
    return s[:-1] + new_last_char
```