Uryuu chose the Wandenreich over the Shinigamis.
Uryuu chose the Quincies over his friends.
After he had given his friends the token and assured them of his true alliance, Jugram appeared. He had overheard everything.
They fought, tearing down the structures, and injuring Uryuu severely in the process. Instead of killing him right then and there, he started talking. He convinced Uryuu that the Quincies would be far superior and just than the current Soul Society. Mainly that the shinigamis would not bring the justice-world-fate that Uryuu desired. The promises Jugram spoke of truly resonated with him in a way he never thought before.
Revenge, modernization, and greatness was promised in a tempting bundle; Uryuu in his hesitation forgot entirely of cruelty, the ugliness, the genocide that the Wadnereich was planning-no he deluded himself into ignoring it. He told Uryuu that there was reason within the madness they were planning to conduct and told him plans that would easily ruin all of Wandenreich. On the edge of bleeding his entire soul out and listening and being persuaded, it felt like a prophecy which Uryuu couldn't decline.
It felt strangely religious, like an angel was preaching to him. Probably it was just Uryuu being delusional from all the blood-loss, but he wouldn't be surprised if that was so.
It was dying bleeding on the white tiles or agreeing. So, Uryuu demanded his friend's safety and happiness and Jugram agreed. The deal was set. Uryuu chose the Quincies because they struck him more ideal than anything the soul reapers could offer.
They went to help Yhwach, bypassing Isshin and his father. As they parted from the bloody scene, the silver arrowhead was heavy and warm in his pockets; condemning him. The look of betrayal on their faces Orihime-Chad-Ichigo hurt deeply, but Uryuu ignored it. He was convinced he made the better choice, and they all fell under Yhwach's great might.
Uryuu took no part in helping the Quincies reform the Soul society, and instead withdrew into his room. He could barely remember what he did, as his mind was plagued with the wrongness of what he committed. He could barely convince himself to bear his own delusions of that he was right, that the choice he made was the right one. Years passed with feelings of hate and sickness. He could recall some moments of happiness in the bloom of Ywach's kingdom, but there was always an underlying feeling of that he was completely wrong, that he made a great mistake and he would pay for it in blood.
Uryuu was informed that his friends were kept in a mansion that absorbed all their reiryoku and sealed their reiastu. From the shadows he would observe them ensuring that their desires would be fulfilled and comforts granted. As time went on the more he would hear Orihime curse at his name and Chad pounding at the mansion walls. He comforted himself that this was the better choice instead of helping them when they begged to be freed. Uryuu could only stand, sickened with himself and with the countless times he tried to deceive himself. It was all he would do, making sure of his friend's (they wouldn't be anymore at this rate, friends that is) well-being and ignored the outside world. He felt untethered and loose; his mind was a mess. The silver arrowhead grew heavier.
He had also heard that Ywach had taken upon himself to teach Ichigo the ways of the Quincy. Ishida nodded, he understood (he pretended he couldn't hear the screams of torture down the halls, and how it sounded undeniably like Ichigo). Once he wandered into one of training rooms when Ywach was gone and all the guards left for a break.
Ichigo was in the room staring blankly at the wall, around him pages of Quincy history and artifacts. The pungent smell of bleach hung thickly around the room. Ichigo stared at him with such unbearably dead eyes and said, "Help me."
Ishida had told him with the unbearable feeling of wrongness, "This is for your own good."
He left Ichigo in the training room and then avoided the place ever since. The silver arrowhead burned.
Finally, it happened that there was no longer anything left of Ichigo. To be more precise everything that made Ichigo was stripped away and replaced with a quincy propagandist. He was no more than an obedient dog that listened to Ywach with his emotions only settling on anger or bloodlust. He hated everything. What confused Ishida the most after Ichigo's reformation was that he hated him. It was a passion Ishida couldn't understand, because Ichigo didn't remember his mother, father, or his sisters, but he remembered Ishida. He remembered Ishida enough to try and kill him or hurt him every time they saw each other. It was only because of Yhwach that a full battle between them never started.
So, Ishida watched the reformed Ichigo from a distance and slowly saw that he was visiting his (not Ishida's) friends at the mansion. He didn't report it. The smell of Bleach, dead eyes, the heavy silver arrowhead. He saw that Ichigo was healing under Orihime's and Chad's care. While keeping watch over Ichigo, Jugram and he spoke often.
Jugram informed him about the current society, which was renamed Wandenreich. Uryu listened to him and tried to believe that Jugram's words were true. The more Ichigo visited the mansion the more he started changing. He grew less combustive and became sullen-thoughtful-quiet. At times when he came to answer Ywach there was a glimmer in his eyes that Ishida could name as a hate disguised as adoration. Ishida knew that glint, as he could see it often in his own eyes when he examines the silver arrowhead.
Even stranger Ichigo began to look at him more thoughtfully and carefully. He would glimpse Ichigo's dark brown eyes out of the corners of his own. Uryu preferred it when he blindly charged to attack him, but he still didn't report about Ichigo's meetings in the mansion which he had been forbidden from. He didn't want to take away the little left for his (once) friends.
Ishida had been summoned by Yhwach for a conference. He (Yhwach) told Ishida that Ichigo had betrayed them and the prisoners escaped.
It was as if he awoke from a dream, away from a pleasant fog of oblivion and saw the truth before him. Ichigo's ever encompassing reiastu had disappeared, and only then Ishida realized that Ichigo's reiastu had changed by extremes. His golden warm color had grown muddled with blue at the edges and became even more wild and untamed than before, like a snake waiting to strike. Ishida rushed to the mansion only to find it destroyed and empty. Ichigo had taken his friends and escaped. When the only thing Ishida paid attention to disappeared, it forced him to invest in something else. With stunning clarity, he tore his eyes away from the ruins of the doll house (more fittingly named than a mansion) and focused on the Wandenreich, once known as the Soul society.
After a few days of snooping it became clear to Uryu that the Wandenreich, no, Soul society was worse than before. Ywach was an uncaring king who wore the guise of compassion and his reign was akin to tyranny rather than kingship. His throne was guarded fiercely by the sternritters who mercilessly killed anything and anybody who posed opposition, and the sternritters were just as worse as Mayuri were, no Ishida would even claim that they were worse. They treated the spirits as playthings and would often execute them for no reason.
The smell of blood and fear stained the Rukongani as spirits perished and bowed their heads in obedience to the tyranny of the Quincies. The sight sickened Ishida, but he couldn't help them. Since the upheaval of the worlds shinigamis were removed and hunted for sport. Ishida had never seen a hunt himself, but he could recall how the reiastu of a Shinigami would flicker out slowly while surrounded by the reiastu of other Quincies. By sorting through the files Ishida found that three of the captains were left alive, Bakuya, Mayuri, and Toshiro. As he continued reading, Uryu found the names of Ruika and Renji within the list of deceased. Bitterly he left the room, driven by the deaths of Shinigami and spurred by the Quincies' cruelty he began a plan to topple Yhwach and take over Wandenreich.
He formed connections with other Quincies that were unsure of Yhwach's rule and spirits with the potentials of shinigamis. The trust between them was unstable and hesitant, but Ishida strived forward. The truth was that Ishida was too late to try and fix the balance. He felt it in his soul, the merging of the living world pressing upon the dead. The feeling of instability, the wavering and the physical screaming of reishi had already warned him that it was too late to save any of the worlds.
Monsters stronger than hollows were forming, taking on the traits of those from Hell and the living. Hollows would suddenly revert back into spirits or random spirits became hollows. Spirits would randomly die or wouldn't die at all. Tremors started to shake the entire world of Wandenreich and each with every tremor the reishi would scream and quake violently. Even the Quincies were starting to suffer from the dying wails of the spirit world. He knew that the world was failing and soon they would all fall into oblivion, but Ishida couldn't bring himself to care for that. So, he did what he was best at, by ignoring it. He could almost feel the arrowhead screaming in his coat pocket.
Ishida was wary, the plan for the upheaval within months. The dying wails of the Soul society had gotten worse, now with every termer the land and the spirits that lived on it would merge and melt together. Anybody who couldn't summon a reiastu platform was immediately consumed by the floor beneath them. The Rukongani was in a state of panic and disaster, and not even the sternritters could keep them under control. Yhwach had summons for them to go and calm down (murder) the spirits. As they were walking down the halls, Jugram stopped the him and cornered him with a sword.
There was a horrible sense of wrongness as Jugram told him that his coup had been found out all executed, and that Yhwach was summoning him to his own execution. Ishida snapped. So, something in him snapped and he melted into his anger and started fighting. He could remember drawing arrows over and over, blood spilling over the white bleached floors. The silver arrowhead heavy against his hip was finally taken out. However, Ishida never got the true chance to use it as memories flashed into his head. He remembered too much, the delusions and grandeur of it all weighed against his head.
For a single second he hesitated, and it was all it took for Yhwach to smash the floor and tilt Ishida's aim so that the arrowhead lodged itself into his shadowy body rather than into heart.
Ishida failed and Yhwach squashed him like a bug, downing him with a flick of his wrist. The force caused him to slam into the once pristine floors and cough up blood. His head was hazy, his thoughts slow. In the last remaining few seconds of his life Ishida realized that choosing the Quincies was the wrong idea. No denial, no excuse, and all the feelings of wrongness made sense. He felt right and had achieved a peaceful state of mind during his last moments. He closed his eyes and breathed his last breath and the future that never was supposed to be ended.