Prior to the Battle of the Concepts, I think Ushijima had a very rigid and linear view of strength. The way he interacts with Oikawa implies that he believes there is a correct path and shows his firm belief in his own strength. Hinata forces him to reevaluate this mindset.

There is the primary Battle of the Concepts playing out between Ukai and Washijo, but there is an individual battle between Ushijima and Hinata. The lucky ones versus the unlucky ones. Traditional strength versus evolution. A solid foundation versus adaptability.

During the match, Ushijima was clinging to his strength, while Hinata had just abandoned his reliable quick to evolve. The line that is the core of Ushijima’s chapter is pure Hinata. It is the entire point of the Brazil arc. He goes back to the beginning to rebuild his strength.

Karasuno, and Hinata, won the battle of the concepts and the effect of that is as clear as day in Ushijima’s current mindset & willingness to abandon his strength. You can see he struggled with it at first, he hesitates and wonders if it was a mistake in a way Hinata never did.

In this way, Hinata was actually the lucky one, because for him there has never been anywhere to go but up. This freedom may have been part of what made Ushijima feel so vehemently towards Hinata.

Hinata sprouted from the concrete, and got to build himself from the ground up, whereas Ushijima was born lucky. With that gift comes expectations and a more set in stone version of your strength, whereas Hinata was a blank slate that could absorb from everyone.

I think Ushijima sees himself in Hinata or rather who he could have been under different circumstances. It’s clear that this encounter had a large impact on Ushijima, and his philosophy today. He embraced the Karasuno philosophy of consuming and learning from others.

Ushijima is now unafraid to destroy his own strength in pursuit of evolution, because he too has learned that strength is being free.