Wizard of Legend

This is really easy all you need is two controllers. After you have completed the tutorial you have access to the chaos trials, you just need to select two player on the title screen, have each controller join the game and start the trial and it unlocked for me during the loading screen.

The other solution works fine, but I found an other way that doesn't require a second controller at all

Equip the offense relic "Friendship Bracelet", which you already have at the beginning of the game in your relic chest. Enter the chaos trials and achievement unlocked !