The function seems to duplicate the first character of the input string and append characters after their respective position in the string in an alternating manner. For example, the output for "hello" is "heoloo"; for the input "fruit", the output is "frxitx".

[CODE]: Here's the Python code that approximates the behavior of the function:

```
def approx_function(input_str):
    output = ""
    for char in input_str:
        output += char + char
    return output
```