A/N: Just a random plot bunny I came up with when I found out that the word Thursday is derived from Middle English Thuresday, which translates to "Thor's day". And with Castiel being the Angel of Thursday, well it spawned a lot of crossover ideas. I have a pretty basic outline planned out but past that this story may or may not be continued depending on how interested people are in seeing it finished.

I'm assuming that in this situation the Avengers Universe and the Supernatural Universe are completely different dimensions, because I think SHIELD would be aware of supernatural creatures if they existed and the whole Thor and Loki are actually aliens not pagan gods wouldn't really mesh well with Supernatural 'verse. Also Supernatural 'verse will be AU because Cas's characterization in the Sixth and Seventh season doesn't really work with what I would like to do with this story.

Warning: I do have some Angel OC's in this story, they don't play a major role, but they're there. Because I know absolutely nothing about Angel Lore I just googled well know Angels then picked and chose names. Also, come on guys, it's Castiel, there's going to be a lot of references to God and Heaven and Angels and just religion in general. If you watch Supernatural, then I'm assuming you aren't easily offended by religious references, but if you are, then be aware my story has them and they're most likely completely inaccurate, so if that bothers you then don't read.

His prayers had been answered. God had spoken to him.

It had been years, but Castiel still found it overwhelming when he thought about it.

His Father hadn't approved of Raphael's arrogance and lack of faith, and had stripped him of his Grace and plunged he and his followers into the pit where Lucifer and Michael dwelled. In the power void left behind by the fall of God's four Archangels, others had been called to step into their positions.

Castiel and his fellow Archangels had been given guidance on how to lead their brethren and then their Father withdrew from them yet again. The Host however had been filled with a new faith and Heaven often shook with the songs of their praise, even though several voices were missing from the choirs.

While seeing to the rebuilding of Heaven, Castiel also had plans to restructure it. He was working with the human Ash in order to abolish the matrix-like lay out of Heaven. Eventually they were hoping for a system in which families could dwell together in their own Heavens and that visiting other Heavens would be something anyone could do.

Heaven was beginning to see its former peace and glory, and so when an outsider entered one of God's worlds, it was immediately detected.

"Brother, troubling news has been brought to our attention," one of Castiel's fellow Archangels said.

Castiel looked up from his conversation with Ash. "What news, Sister?" he asked.

"It would be best discussed in private, Brother. The other Archangels await us," she responded.

"Of course Sister," he said before turning to Ash. "We will resume our work later Ash," he said as he and his sister disappeared, leaving only the sound of fluttering wings behind.

"Wai-" Ash sighed. "Well, his timing still sucks."

Two of the four newly appointed Archangels, Selaphiel and Jegudiel, were waiting for them.

"Castiel, Ariel, you have arrived," Selaphiel said.

"Yes, Brother," Castiel said. "But I do not know why we have been called."

"One of our Father's worlds has been," Jegudiel paused, "invaded."

"Speak plainly, Brother. What do you mean, invaded?" Castiel asked.

"A Jotun, Loki, entered an Earth through the use of one of our weapons. His intentions are unknown, but already several humans lay dead or possessed by his hand," Jegudiel replied.

"One of our weapons?" Castiel asked.

"It fell a long time ago, and its true name is lost to us. The humans refer to it as the Tesseract. It has been away from Heaven for a long time. It belongs more to them than to us," Selaphiel said.

"The kind of power does not belong in the hands of humans," Ariel said.

"Humans are not the problem Sister, what worries me is what this Jotun plans," Castiel said before asking, "Which Earth is he on? The Righteous Man and his brother should be warned if their world is being threatened again."

"Dean Winchester's work is done, Castiel," Jegudiel said, much to his relief. "Loki has chosen a different Earth."

"I don't understand why any Earth has been chosen. We have a treaty with the Jotuns," Ariel said. "Why have they chosen to forsake it?"

"Perhaps they see weakness and have chose to take advantage of it. Our previous superiors recently ignored the presence of an Asgardian on that Earth in favor of focusing on the Apocalypse of another. An entire human town was nearly destroyed and they did nothing to stop it," Selaphiel said.

"A mistake that should not be repeated," Ariel said. "We should purge this Jotun from the Earth and make him an example to those who seek to harm our Father's creations."

"I agree," Jegudiel said.

"As do I," Selaphiel said.

"I have always worked to protect our that which is our Father's," Castiel replied. "But Brethren and Sister, you have been unable to find vessels and your work is limited to that which can be done in Heaven, so it is I that will have to go."

"You also have the most knowledge of human customs, Castiel. We will cover your duties in Heaven and allow Ash to continue his work in your absence," Selaphiel said.

"We know you won't fail, Brother," Jegudiel said sincerely.

Castiel, and the body of Jimmy Novak, landed in a large grass field. A golden beam of sun pierced the clouds, illuminating his silhouette and casting the dark shadow of his extended wings across the length of the grassy area. He smiled as a soft breeze blew through his feathers, before he folded them back into his Grace.

He was glad to be here, despite the gravity of his task. Heaven was his home, but he truly enjoyed his visits to Earths.

His grin faded and a more serious expression took hold as he extended his senses out. This Earth, it was different then the one he had most recently visited. Unlike Sam and Dean's world, which was sewn closely together with Purgatory and Hell, this world instead bordered several alien dimensions, Jotunheim and Asgard, just to name a few. And so while one was assaulted with supernatural threats, the other would face alien invasion.

And the Angels would protect from both.

Castiel gasped in horror as his senses brushed against the Jotun.

Unnatural. Its presence was unnatural, nothing of it was of his Father. Everywhere it went, everything it touched, was tainted. It was worse than demons who had been created by his brother, and at least bore some connection to the Father, and it was worse than monsters, who were still vaguely human and of God, even in their fallen state.

This being was completely alien, completely wrong. Its presence seared the Earth and it would be so easy to track.

Castiel disappeared in a flurry of wings.

"Power at 400% capacity, sir," Jarvis said.

"Well how 'bout that?" Tony said with a grin, before aiming to fire at the irate alien in front of him.

Castiel appeared next to the Jotun, who visibly jumped. Castiel surveyed the being in front of him. It was pale, dark haired and very slim. And so very human looking for something so very not.

"Jotun, you should know that the Earth is under our protection, your kind are not welcome here."

"It cannot be," the Jotun said. "Your kind are a myth, you should not, no, you cannot, how can you be here?"

Castiel almost responded when an explosion rocked the mountain side and what appeared to be a flying metal suit and-his eyes widened, then narrowed. Another one. Not Jotun, something else. Castiel closed his eyes. Asgardian.

And in the suit was a human, it was attacking a human.

Both Suit and Asgardian hit the ground and Castiel flew to meet them.

A/N: Reviews are appreciated, tell me what you think. Is anyone interested in seeing this continued? Also if Castiel seems more formal or Angel-like, it's because he's been back in Heaven for several years now, so obviously he's going to talk and act more like an Angel and less like Dean than he did in the original series.