Sure, here is an example of a Node.js function using ES6 module syntax that retrieves an image from a URL:
```js
import https from 'https';
import fs from 'fs';

async function downloadImage(url, filename) {
  const file = fs.createWriteStream(filename);
  return new Promise((resolve, reject) => {
    https.get(url, response => {
      response.pipe(file);
      file.on('finish', () => {
        file.close();
        resolve();
      });
    }).on('error', error => {
      fs.unlink(filename);
      reject(error);
    });
  });
}

async function getImage() {
  const imageUrl = 'https://example.com/image.jpg';
  const filename = 'image.jpg';
  await downloadImage(imageUrl, filename);
  console.log('Image downloaded successfully!');
}

getImage();
```

Here's how this code works:
1. First, we use the import statement to import the https and fs modules, which we will use to retrieve and save the image respectively.
2. Next, we define an async function called downloadImage that takes two parameters: the URL of the image and the filename to save it as.
3. Inside the downloadImage function, we create a write stream to the file using the fs.createWriteStream method.
4. We then make an HTTPS request to the provided URL using the https.get method. We pipe the response from the request to the file write stream using the response.pipe method.
5. We add an event listener to the file write stream for the finish event, which is emitted when the file has been completely written. When this event is emitted, we close the file using the file.close method and resolve the Promise using the resolve method.
6. If there is an error during the download, we delete the partially written file using the fs.unlink method and reject the Promise using the reject method.
7. Finally, we define another async function called getImage that calls the downloadImage function with a sample image URL and filename, and logs a message to the console when the image has been successfully downloaded.
8. We call the getImage function at the end of the script to execute it.

This code uses modern ES6 syntax and best practices for asynchronous programming in Node.js, and should be able to download images from any valid URL.
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