"I had a system." Joshua claimed. "You are already aware that I am close with nearly every design spirit, right? I can even get along with Ylvaine and the Superior Mother. I always made use of my relationships with all of those spirits to borrow their power whenever it was convenient. My Everchanger is the only Larkinson mech that can switch design spirits on his own initiative. That has given me a lot of flexibility in past battles. My companion spirit Willy strengthens my combat system even further because he can independently call down another design spirit."
In other words, Willy and the Everchanger were able to work together to call down two different design spirits at the same time!
The huge number of possible combinations increased the versatility of the Everchanger even further, allowing him to swap out a seemingly endless variety of advantages whenever it was necessary.