Stein and Mia had made it a rather nice trap. It was a room, with only one closed exit - however frail that exit might be. It was a closed space. Limited movement, and with a maxumum volume, thus limiting the maximum damage output Gilgamesh could dish out. 

However, little did Stein and Mia know that this box was also a trap - on them. 

Mad Dog Junior wasn't even paying attention. Mad Dog Senior was surrounded by lances. Armoured Mad dog was headed right for him. They were all here. 

Good. 

Without even a single motion, Like sheep herded into a slaughterhouse, Gilgamesh unleashed his "weapon." From twenty different directions all around the room the Gate of Babylon opened. The Gate of Babylon was something that existed in the very reality around them; why did it need to be limited to appearing right near the king? The answer was that it didn't. Through those twenty open gates Gilgamesh's weapon came out. 

Water. 

In the small millisecond between sight and comprehension it might seem like the King of Heroes had decided to drown them all. That statement would be supported even more when the water completely engulfed the room within a matter of 2 seconds, submerging everyone and everything with "water". However, it would soon be clear that what the King of Heroes had summoned was not mere "water", but something much more powerful.

Aqua Vitae. 

It was the ultimate secret of alchemy. All afflictions of the soul, mind, and body are washed away by the purity of this liquid, and their bodies would be completely restored to full health. Gilgamesh allowed the water to remain in the room - as a heroic spirit, he was completely fine in the water he himself had called - watching the submerged panic for around two seconds like a cook watching his soup boil before draining the water, which disappeared as fast as it appeared. 

Not even the fear wavelengths of the Kishin Asura could resist the purification created by Aqua Vitae. Those with the black blood would find their darkened blood gone, their bodies repaired to normal. Those who were insane would find themselves sane again. Berserker would lose his mad enhancement. Stein, Mia and Weiss would find the Black Blood gone, as well as their insanities, their madness.

And above it all, standing in his perfection, allowing the last drops of Aqua Vitae to drip down the shoulder pads of his golden armour, was Gilgamesh, slayer of the "mad beasts" that were Stein and Mia.