The Quincies in Bleach are some of the most fearsome foes that have been ever introduced in the series. In the Bleach manga, fans got more of a chance to see just how powerful they are, and among them, Uryu Ishida is easily one of the strongest of them all.
When Uryu was first introduced in Bleach, he was without a doubt a spectacular character. But it was made clear as the series rolled along that he wasn't as strong as others in the franchise. While he did have some impressive moments, such as taking down the Captain of Squad 12, Mayuri Kurotsuchi, Uryu otherwise regressed as a character from his first appearance. Fans of the show and manga got to see Ichigo's frightening potential continue to skyrocket while Uryu seemed to fall further by the wayside. It wasn't long before he became an afterthought -- a sidekick at best for some of the most intense battles in the Bleach universe.
Uryu has, without a doubt, shown himself to be a valuable and useful ally, but unfortunately, his value is placed more on his intelligence and not strength, which is too easy to overlook. But Mangaka Tite Kubo gave fans hope that Uryu would once again return and become an integral, action-oriented part of Bleach again when the Quincy finally regained his lost powers just in time for the "Hueco Mundo" Arc. He fought valiantly, defeating the powerful Arrancar, Ciruci Sanderwicci before being bested by the more skilled 8th Espada, Szayelaporro Granz. These two battles revealed that Uryu had indeed gotten much stronger -- but it also proved that he had a long way to go before he could be considered one of the strongest fighters in the anime.
In his next major appearance, Uryu was reduced to playing caretaker for Orihime while Ichigo fought to the death against the 4th Espada, Ulquiorra Cipher. While he did have some cool moments, such as momentarily taking down Yammy Llargo -- who was considered to be one of Aizen's strongest Espada -- Uryu was once again proven to be mere cannon fodder. This cycle would continue on for some time as Uryu's true potential continued to be hidden from both the viewers and readers of Bleach. In an almost annoying fashion, it seemed that battle after battle, Uryu was destined to forever play the role of scapegoat for the stronger and more important characters. That was, until the "Thousand-Year Blood War" arc.
With the arrival of the Quincies, fans saw a shift in Uryu's character. One of his fellow Quincies, Quilge Opie, even remarked to Ichigo that it was impossible for even his powerful Quincy abilities to even come close to Uryu's. This revealed that either Uryu had been holding back, or he didn't have access to his full abilities during the course of the anime. What is even more impressive is the fact that Quilge was able to lay waste to multiple powerful Arrancar while also almost successfully detaining Ichigo. Furthermore, when Uryu makes the decision to officially join the Quincies in their war against Soul Society, there are even more secrets about his strength that are revealed.
When the Quincy king, Yhwach finally made his return after centuries, he specifically chose Uryu as his successor. It was revealed that Uryu was a half-blood Quincy who survived Ywach's attempt on his life as a baby. This was so that the Quincy king could regain his powers, but Uryu was the lone half-blood Quincy that was unaffected, making him a very unique case, even amongst full-blood Quincies.
Uryu was the only Quincy in existence to ever be able to resist the king's immense power. This skill is known as Antithesis -- a dangerous ability that allows Uryu to reverse something that has already happened between two targets. The ability was so powerful that even Yhwach himself stated that Uryu's powers would one day evolve and surpass his own. The best example of Antithesis being used is when Uryu was mortally wounded by the king's Grandmaster, Haschwalth, where he was able to use his powers to reverse the damage and heal himself while transferring his grievous wounds onto his enemy. It is a terrifying feat to have at someone's disposal; one that essentially makes Uryu one of the most dangerous and powerful characters in all of Bleach.
Uryu Ishida's character path in Bleach took many twists and turns, even the loss of his powers completely at one point. But though he has been vastly underpowered at some points in the series, he ended up becoming far more than just Ichigo's underappreciated sidekick by the manga's end.