The Hyrulean armies pursued the monster army, slowly getting closer, but previously, both times they were about to close in, Astor would leave some of the monsters behind to slow them down. This was the third time, and they expected the same result.
This time, however, the monster army turned to face them in earnest. Either Astor had realized he would bleed his army dry trying to outpace the Hyrulean armies, or now that the Hyrulean armies were in the open field, they were vulnerable. Either way, Astor had realized he could encircle the Hyrulean forces, given that his forces outnumbered theirs. It wasn't as successful as Astor had probably hoped, but a lot of soldiers got tied up guarding the flanks.
Suddenly, the gates of Hyrule Castle opened, and a force of monsters started charging towards them from behind. And not weak ones either; black, silver, and golden Blins and Lizalfos, powerful Wizzrobes, armored undead that were known as Darknuts, ReDeads (some of which seemed to be on fire and yet not burning), Guardians of all sorts, a Black Hinox, and several Lynels. Enough to devastate the Hyrulean armies if they reached their rear.
But they never did, because King Dorephan interposed himself between the attack force and them. "I am Dorephan, King of the Zora!" the massive monarch shouted. "And you! Shall not! PASS!" With that, he charged at the attack force, caught the Hinox by the throat, and threw it at the other monsters. He then started tearing into them, killing them by the score with every sweep of his massive trident. Very few of them made it past him alive, few enough that they couldn't attack the Hyrulean army in any kind of numbers that could be a threat.
The monsters, however, did not idly let the Zora King slay them. Arrows, spells, and Guardian beams were all fired at him, many of them finding their mark. But King Dorephan kept fighting as if they didn't even faze him.
Dedue, Flayn, Hilda, and Sidon, not being fast runners, had ended up as part of the rear-guard by virtue of being there, and they took down several of the stronger monsters that made it past Dorephan. Sidon clearly found it hard to watch his father take so many attacks, but it was doubtful that anyone could get close to Dorephan without either dying or forcing him to hold back.
In the front, things weren't going as well as they could have been. While the front line was holding the line well, for every monster they killed, there were always more to take their place. And while the Hyruleans fought admirably, there were an unfortunate number who fell and never got back up.
That didn't stop them. Linkle's boot caved in a Darknut's helmet, as her Cuccos swarmed a Lynel, distracting it for long enough and injuring it enough for Riju to smite it with lightning. Sooga cut through a Hinox's leg, while Ashe sniped the eye right out of its head. Volga leapt onto a Talus using his wings and shattered its ore deposit with a single blow, Robbie's remote-controlled Guardian wiped out scores of monsters, Raphael and Balthus held a Lynel still as Kronya delivered stabs to places that could be sites of critical injury until it died. But it was clear that at the current rate, the Hyrulean forces would be the ones to lose.
But then, something strange happened. Dozens of Guardians were pointing their targeting beams at the Hyrulean forces, only to abruptly change targets. The Guardians began attacking the monsters, their legs sweeping away the small fry and their beams exploding against the powerful ones. A few Guardians did not turn, but only the ones completely covered in Malice; every one of the less-corrupted ones turned against the monster army.
"She did it," Impa realized. Indeed, Purah had cracked the control code, and had found a way to purge Ganon's corruption from within them.
For the front line, it was a welcome sight, but not one that changed the tide of the battle. Many monsters died or were injured by the Guardians, but there were always more, and the Guardians were torn apart in short order. However, at the rear, the Guardians devastated the strike force coming out of Hyrule Castle. Guardians massively outnumbered the other powerful monsters in the strike force, and the Lynels among them that hadn't been killed by King Dorephan quickly found themselves doing a very convincing impression of a sponge. ("Was that the most fitting description, Hilda?" "Yes. Shut up.") And the Guardian turrets on the walls began raining down blasts of destruction on the monsters on their way to try to strike a blow against King Dorephan.
With so many of the small fry on that side having been crushed by King Dorephan, there weren't really that many left in or near Hyrule Castle. It seemed that by the time they destroyed all of the Guardians, there wouldn't be nearly enough left to launch an attack on the Hyrulean army's rear.
His goal accomplished, King Dorephan let the life leave his body. He fell to his knees, but no further. Even in death, he remained upright, a picture of a true warrior king. Many of the monsters didn't even realize he had died, and kept attacking his corpse.
"Father..." Sidon said softly and mournfully.
King Dorephan would be remembered as a titan, a warrior who could not be felled even by the reaper himself. But even a death of such significance could not stop the fighting.