The function takes an input string and replaces vowels with the next vowel in the sequence (aeiou), replacing 'u' with 'a'. Consonants remain unchanged.

[CODE]:
```python
def vowel_replacer(input_string):
    vowels = "aeiou"
    result = ""
    for char in input_string:
        if char in vowels:
            if char == "u":
                result += "a"
            else:
                result += vowels[vowels.index(char) + 1]
        else:
            result += char
    return result
```

Please try running the function with more inputs if you'd like, or let me know if you need any more help!