Before we jump in, let's make sure we've got everything we need to use Supabase with Koa.js. You'll need Node.js and npm (node package manager) installed on your computer. Also, don't forget to create a Supabase account if you don't have one yet.

First things first, create an empty directory for your project and navigate into it using the command line. Then, initialize a new Node.js application by running:

npm init -y

Next, let's get Koa.js installed by running:

npm install koa

At the same time, install the Supabase JavaScript client library via npm by running:

npm install @supabase/supabase-js

Create a new file, let's call it server.js, and set up a basic Koa.js server. Here's a simple example to get you started:

const Koa = require('koa');
const app = new Koa();

app.use(async ctx => {
  ctx.body = 'Hello World';
});

app.listen(3000);

First, import the Supabase library into your server.js file:

const { createClient } = require('@supabase/supabase-js')

Then, initialize Supabase by passing in the URLs and keys from your Supabase project's settings. You can find these in your Supabase dashboard under: Settings > API.

const supabaseUrl = 'https://xyzcompany.supabase.co'  //Example URL
const supabaseKey = 'public-anon-1234'    //Example Key
const supabase = createClient(supabaseUrl, supabaseKey)

Now you can use Supabase inside your Koa.js routes to interact with your Supabase database.

app.use(async ctx => {
  let { data, error } = await supabase
  .from('profiles')
  .select('username, website, avatar_url')
  if (error) {
    console.log('Error: ', error);
    ctx.body = 'An error occurred';
  } else {
    console.log('Data: ', data);
    ctx.body = data;
  }
});

In the code above, profiles is a table in the database. Replace it with your own table name and adjust the select query according to your table structure.

This was a straightforward example of using Supabase with Koa.js. For more complex operations, using middlewares, error handling, and more intricate routing logic with Koa.js and Supabase, refer to their respective documentation.