Ruler
Even though the Grail was partially corrupted by Angra Mainyu, there still was a part of it that was Holy as it had been on the day the artifact was manifested into the reality by the combined efforts of the three families. And this part of the Grail could feel that something needed to be done to keep the summoned spirits under the control, for those like Caster, if left unchecked, could cause great amounts of destruction for no other reason than destruction itself.
It took the grail a lot of thinking, but in the end it came to a conclusion that no human-born spirit from the Throne of Heroes would be enough for the task. No, someone on the whole different level was needed. So, the Grail turned its attention to the lore of humanity – after all, the myths of one reality were always the true history of another... After a lot of searches, the perfect candidate for the role of the war overseer was found. And even though the Grail found some difficulties in manifesting that entity into the world, the Fourth war now had someone to keep the seven heroic spirits in line...
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For quite some time things progressed normally and Ruler saw no real reason to intervene. Sure, the battle in the docks had been a light-show that could be seen for miles – Rider wasn't really trying to be discrete with his flying chariot that shot lightnings everywhere – but none of the heroic spirits involved in that fight had stepped out of the bounds imposed on them by the rules of the Holy Grail war.
Even with Caster was causing quite a lot of problems with kidnapping and killing children around the city there were no reasons for Ruler to step in: at the moment it was still within the rules of the war, no matter how much Ruler disliked the fact that something as horrible as this was allowed... It was all within the rules of the damned Holy Grail War, and so he just continued observing.
But when Caster tried to summon an evil monster from another dimension, intent on letting it devour both his opponents and the Fuyuki city altogether, Ruler could no longer stay hidden and out of the war. This time Caster had overstepped the bounds and needed to be dealt with...
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Saber, Lancer and Rider watched in fear as the Ktulhu summoned by Caster slowly crawled towards the bank of the river. So far this demonic monstrosity proved itself to be essentially invincible. No, it did take damage from the servants' attacks, but it regenerated its damaged flesh before either of the tree heroic spirits could make use of those wounds... Archer's ability to rain infinite weapons upon his desired target might be able to eventually slay the beast, but the golden bastards was way too busy having his fun in the dogfight with F-15 jet plane hijacked by Berserker to help the noble trio out.
The situation was getting so desperate that Lancer was ready to destroy one of his noble phantasms – his Gae Buidhe lance – to let Saber heal her hand in hopes that her anti-fortress Noble Phantasm will be able to reach and destroy Caster hiding somewhere in the fleshy depths of the monster he had summoned.
"Heroes of the war." A deep voice suddenly spoke next to the trio, causing them all to immediately turn their attention towards the newcomer. He was a rather average in height bald dark-skinned man with golden eyes. He was dressed in slight-worn golden armor that most definitely wasn't created by mortal hands, along with a khaki cloak billowing behind him in the wind. In his right hand, the newcomer held a sword even more majestic than Excalibur itself. And just like the stranger's armor, this weapon too wasn't created by mere mortals. If anything, it looked like the sword had been forged somewhere in the Heavens. "The Grail had deemed Caster to be a rule-breaker and ordered me to stop him." Now it was masters' turn to stare at the warrior: none of them was aware that the Grail had this sort of a safeguard. "You will be allowed to continue your battles after this monster and its summoner are defeated." Somehow, this man spoke with such authority that even Archer and Berserker stopped their dogfight.
"C-Can you really defeat this thing?" Waver Velvet asked in a shaking voice. Sure, even someone like him could feel the power radiating from this man, but will this power be enough where three servants had failed?
"On my own... No, I'm but a single warrior." The warrior replied. "But those following me shall be able to defeat this demonic spawn." As the unknown man spoke this, his clothes changed: first, a hood appeared, covering his face so completely that only black void could be seen. The man's armor became all-new and sparkling while his cloak turned pure white. Then a pair of strange ...attachments appeared on his back – they looked like a metal curves pointing towards the skies. And another moment later a multitude of ribbons of white-blue light burst forth from these 'curves', forming something akin to wings behinds the stranger's back.
At this very moment, somewhere up in the air, Gilgamesh finally admitted it to himself that here, in front of him, there was a being greater and more powerful that he himself was. It was not an easy thought for the golden-clad Archer of the Fourth Holy Grail War, but he'd be the greatest fool if continued denying the truth when it stood right in front of him.
"W-Who are you." Irisviel asked the angelic being that was now hovering several inches off the ground in front of her. The winged man turned his head to look at her – even though the Einzbern homunculus could see nothing but darkness under his hood – and, after a long second of pause, gave her the answer.
"I am Justice." The strange Servant's voice was now much deeper and had even greater power to it, while at the same time coming from no distinct direction... The Angel turned his attention back to the Ktulhu which was slowly wadding its way towards the Fuyuki city. "Warriors of High Heavens, answer the call of your general!" The unknown man spoke as he had raised his sword towards the skies.
Suddenly, a good hundred of light beams pierced the heavy clouds which were hiding the night sky. And from using these beams like one would use a road, winged warriors of Heavens poured into the mortal world. Within seconds, the sky became filled with literally thousands of angels. Once the winged warriors were all there, their general lowered his sword till it was pointing at the Caster's monster, which was still moving across the river.
Heeding the unspoken order, the Angelic army attacked the Ktulhu, flying so fast that they became nothing but beams of light to the onlookers. And while each of the angels could do no more damage than a Servant, the sheer number of them was enough reduce the grotesque but great beast to something that looked like a giant chunk of meat that went through a bad blender.
"There you are." The Angelic general spoke, before too disappearing in a beam of light. A moment later he was seen shooting through the belly of the demonic monstrosity. When he could be seen normally again, he was hovering on his wings of light high above the river, his sword piercing both Caster and his spellbook. A moment later those two began fading away, while the Ktulhu, no longer having the source of prana to keep itself alive in this world, started slowly falling apart... Soon, the beast was completely dead, fallen apart into slowly disintegrating chunks of demonic flesh.
Once the Stranger could see that the monster they were fighting was defeated, he – still hovering in the air – assumed a praying pose, his legion of angels following his example, and they all mourned their fallen comrades: several angels got killed by the Ktulhu's tentacles in the beginning of the fight.
"The Justice has been served." The Angelic general finally announced, before bowing his 'head'. His army returned the bow, before ascending towards the heavens. When they all were gone, he slowly flew to the levee and as soon as his feet touched the stone, he reverted back to his 'human' form. He then approached Saber, who was still looking at him in awe. "Give me your hand, young lady." The Angel commanded. Arturia, following the order somehow without even a thought, began raising her right hand, but was soon stopped. "The other one, please." Holding her left hand in his own tightly, the strange man suddenly drew his angelic sword and ran its tip right along the wound from Lancer's Gae Buidhe. "The curse if lifted." The unknown heroic spirit announced as he let Arturia's hand go, while sheathing his sword. "My presence here is no longer required. May this Holy Grail War continue." He announced then, before turning around and walking away.
He hadn't even disappeared completely, when the air was once again filled with the sound of explosions, as Berserker was doing his best to blow Archer's flying chariot, Vimana, out of the skies...
Ruler
True identity: archangel Tyrael, aspect of Justice, aspect of Wisdom
Series: "Diablo" universe
Age: unknown, immortal
Sex: Male
Alignment: Lawful Good. Well, he is Justice incarnate...
Strength: A
Endurance: A+
Agility: B
Mana: A
Luck: D
Independent action: C - But can be considered Ex as he's manifested into this world by the Grail itself.
Magic resistance: B
Battle continuation: A - Nothing short of a decisively fatal to a human wound can stop him. Temporarily.
Divinity: Ex - Archangel, aspect of Justice, aspect of Wisdom. Tyrael is a being on the level of a God.
Discernment of the poor: A - Tyrael got this skill upon taking the mantle of the aspect of Wisdom.
Noble Phantasms:
El'druin: the sword of Justice: B++, item.
Angelic sword that is capable of destroying anything that isn't righteous and can cut through both matter and magic. The level of damage done by this sword is proportionate to depravity of the target. Only true saints and Tyrael himself are completely immune to the effects of this sword.
Archangel: A, support, permanently active.
Following the fall of reincarnated Tathamet (Diablo), Tyrael had accepted his wings back and is once again a full-fledged archangel. This means that he is capable of otherwise-unaided flight. And since he's an aspect of creation, he can't be truly killed even if his body is atomized. It may take him some time, but eventually Tyrael will reassemble himself back to his full glory.
Ten thousands spears: the angelic legion: Ex, anti-army.
In times of need, Tyrael can call forth an army of the High Heavens. While these angels do not possess anything that can be considered a true noble phantasm and can actually be killed, each of them is at least a match to an average heroic spirit.