You saw Loki's eyes widen. He recognized what Odin's words meant, what The Trial of Yggdrasil's Pools was. You recognized the term. It was in the back of your mind, like a distant fleeting memory. It was something you'd learned about or heard about once upon a time, but for the life of you, couldn't remember what it was. Though you knew you knew it. It had probably been something you learned about in your training 900 years ago.
Whatever it was, it had Loki on edge and that couldn't be a good thing. Even Frigga was surprised by that decision from Odin.
That definitely couldn't be a good sign.
Loki could be paranoid and jump to conclusions. Frigga was always even-tempered and gentle. It was hard to shake her calm. Whatever this trial was, it had her concerned. Which in turn had you concerned.
You straightened your spine, preparing for a battle.
Thor, of course, was the first one to step onto that battlefield. It was just in his nature. "What is this trial?" he repeated, demanding more clarification as to what would be expected of him, what he and Loki would have to do.
A thousand ideas went through your mind. A thousand tortures and horrors. A thousand terrible trials. Your own terrible trial went through your mind, snippets of fighting ghasts in Helheim and escorting souls, a month of torture to prove yourself worthy of being at Loki's side for eternity.
You survived your trial. Surely Loki could survive the one he was about to face.
Hopefully both brothers did.
You loved Loki with all of your heart and soul. You had since you were children. But you loved Thor too, he was the older brother you weren't born with, but who was your brother all the same. You didn't want either of them dead, or worse, from this trial.
And you weren't sure you could survive if Loki died.
Then the name of the trial clicked and you practically breathed a sigh of relief. Odin gave Thor a disapproving look, he was upset that Thor hadn't remembered the trial and what it entailed. Clearly, Thor had been taught as part of his preparations to become king. And he either had forgotten or, more likely, never learned the lesson. He was never one for book learning unless it was mandatory. Hel, he took Groot as his foreign language when you were children. It was practically the easiest language there was.
Odin finally spoke when Thor looked properly horrified that he didn't remember the trial. "You and your brother will head to the pools at the base of Yggdrasil. There you will drink of the waters and the fates will determine which of you shall be king," he explained. It wasn't really much of an explanation. He was leaving something important out.
It wasn't the fates, as an incorporeal construct, that would be determining who would be king. It would be the Norns themselves.
Thor didn't understand, but Loki did and you saw him gulp at the prospect of facing the Norns themselves.
"Go, now," Odin told them firmly. After all this time, he wanted this decision finally made.
You all bowed and you left with the boys, striding confidently from the room. You didn't feel that confident, but at least this was better than some of the alternatives your mind had already come up with.
Frigga met you outside the throne room. Somehow she'd beaten you there. You'd stopped questioning how Frigga did anything centuries ago. She hugged Thor and Loki in turn. "I'm sure you will both do well. Do not lie to the Norns," she warned Loki, though even he wouldn't think to lie in front of the Norns.
"The Norns???" Thor asked horrified.
Loki looked over at him and rolled his eyes. "Who did you think we were facing?"
"Father said 'the fates'," Thor said with every Asgardian's learned fear and awe of the Norns in his voice.
"The Norns are the fates, oaf," Loki replied, more terse with his brother than usual due to his own fear. You took his hand and squeezed it, a silent reminder to behave. Loki sighed and hugged Frigga again. "We should get going," he told Thor.
You hesitated. You weren't exactly welcome at this trial, but didn't like the idea of Loki facing it alone. So you took his arm and together the three of you made your way down to the lowest levels of the palace to the temple where Yggdrasil's ponds were located and where the great tree grew up through the palace.
One of the mages was there waiting for you. He bowed to the princes. "Welcome, Prince Thor, Prince Loki," he offered you a bow as well. "Lady Valkyrie," he greeted you all. He turned his attention to you. "You may witness the trial, but you may not interfere. The same rules apply to the Allfather and Allmother." Odin and Frigga were indeed entering the room behind you. The mage turned his attention to Thor and Loki then and directed them to two pools. "Each of you will choose a pool, both are equal, that is not the test. You will drink of the pools and submerge yourselves in its waters. Then the Norns themselves will appear, will test you body and spirit, and determine which of you will be the next Allfather," he explained. Thor and Loki both nodded their understanding. You squeezed Loki's hand reassuringly.
You kissed Loki softly before he dropped your hand. He strode forward with Thor and they paused between the two pools. You couldn't hear what was said between them, but they clasped arms and clapped each other on the shoulder before they turned and each waded into one of the pools. At nearly the same time, they cupped their hands to lift the water to their lips and drink it before submerging the rest of the way into the pools. The pools began to glow with magic.
You finally understood how Loki had felt all of those centuries ago when you faced your own trials.
There was absolutely nothing for you to do but wait helplessly while the trial began.