Acqua assumes 50% of incomplete WW3 Gabriel’s power

That situation was not normal. It was true that it was theoretically possible using the proper methods, but it was still astounding that power that could massacre every single human on earth could be used so easily. But then, an archangel was an archangel. That was the existence that had announced the conception of the Son of God, that received great awe at being deeply related to the beginning of the Christian Church, and was feared as the one that carried out punishments on evil cities. Even a Saint or a member of God’s Right Seat could not win in a straight fight against an opponent like that. In fact, it was unclear if that archangel could be defeated if every single power of humanity were to work together. To put it bluntly, that archangel alone held the power to end World War III. It wasn’t an issue of winning or losing. The war would be “ended” by being thrown into a situation where the war could not continue due to every force in the war being slaughtered. (I see. So that is why Fiamma has grown so arrogant.) William Orwell gave his frank assessment. And even then, his will did not even know how to waver. (But have you forgotten what I rule over as a member of God’s Right Seat?).
(Toaru Majutsu no Index Volume 21, pg 89)

“Oh?” Acqua laughed, and Fiamma lost his smirk. “Then I shall show you a way to stop her without force.” In an instant, Misha Kreutzev’s power was cut by a third. The form of an angel was basically a mass of energy, they had no physical body. More accurately, their bodies were not composed of physical matter. Fiamma, who was linked to Misha, was suddenly dealt a blow through his five senses. “You! ...What did you do...? No! This is...!?” “Have you forgotten? I am Acqua of the Back. A member of the most secretive Roman Catholic organization, God’s Right Seat. I hold the position of the back, and am associated with the color ‘blue’ and the moon. I also wield the power of one of the four archangels, Gabriel.” “You! ...Did you, in your own body...!?” “For Christians, releasing and sealing Telesma is a basic among basics. Also, my body is the strongest link to Gabriel, being “Acqua of the Back” of God’s Right Seat. Therefore, if I forcefully took out the water affinity Telesma within myself, I would not want to think of what would happen to Gabriel from whom such power stems.” “...” It was impossible to imagine that such a plan could have been thought up by a sane man. To forcefully contain the power of an archangel within a mortal body was pure foolishness, even for magicians; for the human body would certainly explode from trying to contain such power. However... “It is not impossible.” Acqua’s voice shattered the silence. “Right now, the Russian nun you are using, she is able to do a similar thing to what I am.” “You are insane! Sasha Kreutzev is only able to perform such acts because of the Telesma remaining in her body from the events of Angel Fall! Even if you duplicated her, you wouldn’t get the same tolerance!! You don’t have that sort of ability.” “Hmph, don’t talk like that... What others can do, I can do too.” So it has come to this, Fiamma thought. He should have known. As a member of God’s Right Seat, it was stupid for Fiamma to have tried to apply normal reasoning to Acqua. “Then... show me!” Fiamma shouted out the challenge. “That I shall.” “You know right? This stupid plan of yours will destroy your combat ability. You are just destroying yourself by trying this.”
(Toaru Majutsu no Index Volume 21, pg 151-152)

A tremendous amount of energy flowed towards him. Under the dark blue sky and shining full moon, Acqua began absorbing the enormous Telesma of the angel. “Uuuuwwwoooooooooooooooooaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa!!!???” Power flowed into him from every pore on his body. This amount of energy could not be tolerated by a human’s body. Just like how a fan could only suck in a predetermined amount of air. If you forcefully tried to take in more than your limit, the consequences would be dire. Blood started pouring out from his legs and chest. It felt as though the muscles on his back and neck were on fire. Blood vessels throughout his body were bursting, and his nervous system was going into overload. The man could feel the tendons and ligaments throughout his body snapping one by one. His legs were shaking, as his once powerful body was on the brink of collapse. However, he did not fall. The sword stuck in the ground, and the willpower in his chest. By relying on those two things, the man was determined to stay standing. The destruction was not limited to just his physical body. His magical power was slowly burned out of him. The man was a Saint and a member of God’s Right Seat. Those two traits of his gave him tremendous power, surpassing that of other magicians. However, now the source of his body was being torn apart and he was losing his magical prowess. His body screamed at him to stop this madness, but the man would not stop until he achieved his goal. Only by absorbing the Telesma of the angel in his body, could he weaken the enemy. To lessen the chance of the Telesma meant to save people being used to take human lives. That was all he wanted. As long as he could ensure that, the man would be able to clench his teeth and battle with the overwhelming tide of Telesma. And then...
(Toaru Majutsu no Index Volume 21, pg 152-153)

Fiamma of the Right smiled. The amount of Telesma Acqua of the Back had absorbed from Gabriel was only about half. As he had foreseen, it was not enough. Unless it was a special circumstance like Sasha Kreutzev, you could not completely absorb an entire angel. “Even 50% is enough to attain victory.” Fiamma sighed in a bored voice. “You power as a Saint and God’s Right Seat, both are gone. This is over now. You gave your life in vain. Kill him.”
(Toaru Majutsu no Index Volume 21, pg 154)

Fiamma of the Right noticed. There was one more person, currently not on the battlefield, an existence who wielded the supreme power. “That bastard!”
(Toaru Majutsu no Index Volume 21, pg 155)

It was a sound the brain of a human could not comprehend, but one could tell it was different from a simple scream. The cry contained unfathomable emotions. Misha’s body, already straining to maintain a humanoid shape, simply collapsed, returning to a state of pure energy. It was an immense amount of energy. A bomb.
(Toaru Majutsu no Index Volume 21, pg 156)

Acqua of the Back, after confirming the dispersion of the mass of Telesma, slowly let go of his giant sword. His entire body was soaked in blood. His strength had vanished from his body. Finally, he collapsed to the ground, his great sword still impaled in the ground. Acqua had a slight smile on his face. He had achieved his goal. He had dispersed some of the archangel’s Telesma, and given Fiamma’s foes a fighting chance. Even though Fiamma wielded immense power, he was too overconfident, and would underestimate the power of the factions that had allied to fight against him. Just like Acqua himself used to be, he mused. Acqua’s internal systems were a mess, and the last traces of magic had been burned out of him. He estimated that he himself would not live for much longer. Well, at least he would be dragging the archangel along with him. He had done enough.
(Toaru Majutsu no Index Volume 21, pg 158)

With a cough that racked his body, and sent more blood spewing out of his mouth, Acqua stood up once more. His powers as a Saint had gone. His power as a member of God’s Right Seat had also been lost. His body had been ravaged. He was now a normal human. Clenching his teeth, Acqua pulled out the last vestiges of magical power hidden within him. It was only enough to keep him standing and prevent more blood from coming out of his wounds. He had not much strength left, not nearly enough to wield his giant sword. However that was not important. A real hero was definitely not one who gave up. He was one, who upon hearing the support of the people, would get back up, no matter how many times he had fallen to his knees.
(Toaru Majutsu no Index Volume 21, pg 161)

Acqua of the Back used their common command over water in order to forcibly strip the archangel’s power by guiding the Telesma making up Misha’s body into his own body.
(Toaru Majutsu no Index Volume 22, pg 3)

Acqua was no longer a Saint. Nor was he a member of God’s Right Seat. He did not have the physical strength to swing up his own greatest weapon of Ascalon and the amount of magic power he could refine was only on the level of an average magician.But what did that matter?Acqua was not fighting because he was a Saint or because he was a member of God’s Right Seat. He did not feel that he had lived a praiseworthy life, but unfortunately, he had a lingering attachment to that world at least to the extent of being able to think of someone he wished to protect.
(Toaru Majutsu no Index Volume 22, pg 95)