Thor tries to visit Mimir and finds more than he wanted.
Thor looked up at the highest peak of Midgard.
'He's up there, but what do I say to him? "Hey Mimir, I'm sorry I didn't believe you about my sons, and I've traveled from the future where Fimbulwinter and Ragnarok happened, and I need your help?'
Thor sighed as he began his ascent. Maybe he could clear his head and try to figure out what to do.
"Let's go over what I know. Baldur was sent to track the Last Guardian, he was stopped by Kratos, he came back to ask for my sons.' Thor paused trying to hyperventilate.
'Magni was killed, I beat Modi and he ended up dead.' His breathing quickened.
'Baldur dies, Fimbulwinter happens, Odin instructs me to distract Kratos while he talks to Loki. Somehow he gets Loki to come to Asgard, we get that mask piece, Heimdall is killed.' Thor almost wanted to stop climbing, He jumped to a ledge.
'Heimdall wasn't always an asshole, and even if he always saw the worst in people, he was his brother. I'm the eldest, wasn't I supposed to be there for them? Sure Hodr, Vidar, Vali, and Bragi were left, but to lose even three of them hurt so much.' [1]
Thor kept going until he saw something familiar; it looked like a Giant sanctuary of old, or at least the mouth of a giant. But in front of it stood an impenetrable black mist and he didn't want to take any risks. He looked at his stomach, his wound that had a hard time healing hadn't changed all that much.
He couldn't exactly fly without Mjolnir, but as much as he adored the weapon he saw as a friend, he was both a god and warrior long before it was made for him. Thor steadied himself and called up his remaining strength, he might have to jump to try and make it. [2]
A loud roar could be heard, Thor turned to see if it was Hymir again, instead, it was a prospect much more frightening. It was Dagsetr, Baldur's dragon, and moved ever closer as its wing beats could be heard across the sky.
The dragon landed, and a skinny and ragged familiar figure stepped off of it. It was someone he had seen in what almost seemed like forever, it was his brother Baldur.
The younger god lazily walked toward him, sizing him and up and down putting his hands on his chin. "Brother is that you? What the Hel happened to you?"
"You know me, I love a good drink." It pained him to say that, it caused him nothing but trouble. It all started with the Long War, drinking became a tool to escape the horror of it. He hated the blood, the screaming, especially when they could barely fight back. It wasn't duty or even sport, just murder.
Baldur seemed to frown. "To the point, you look like shit, even for you?" Thor only laughed, as if he had heard the funniest joke. "Come on, I don't have all da-." Baldur was cut off from his brother's arms tightly wrapping around him. He couldn't feel any physical sensation but he knew he couldn't move free from his brother's grasp.
"Brother." Thor began crying. "It's so good to see you again."
Baldur sighed in frustration before hugging him back, his arms barely reaching around his older brother's back.
"You know I'm on a mission, shouldn't you be back in Asgard? Why are you here, and don't have a way back there?"
The thunder god froze for a moment.
"What the Hel happened to you? You get into a fight with Sif again?" The older god tried not to tense up. "I don't get why you tell me to go seek out Nana if-."
"No, I just made some mistakes. So where are you off to?"
Another sigh left Baldur's mouth. "Fine, come along then, I'm going to see Mimir before Odin pays him a visit."
'Hm just where I need to go, but how do I explain this to anyone back home?'
"How is this mission going?" It was a question Thor knew the answer to as he climbed on the dragon's back.
"This tattooed man put up a fight, they looked like they weren't from around here, but they must have been a giant. They certainly weren't mortal. No one has ever given me too much trouble before."
"Thinking of asking for help?" When his brother first visited Mimir he did it alone, he then returned to Asgard when he couldn't find them for two days bringing Magni and Modi. [3]
"Hmph." His brother just raised his middle finger at him. "The 'Smartest Man Alive' should have answers. I don't want to imagine Heimdall's smug face."
"Neither do I." Wondering what would Heimdall would say about his thoughts was something he didn't want to think about just yet
Dagsetr started to growl, ah approached.
"Easy boy, calm down. He's my brother."
"I'm not that heavy am I?" Thor always liked when Baldur genuinely smiled, and here he was.
"Hah, maybe you just smell." The Thunder God just kept laughing, even as the dragon took flight. It took some time to for Thor to orient himself, usually, he used to ride a chariot pulled by Tanngrisnir and Tanngnjóstr, not something as fast as a dragon. [4]
The dragon quickly pulled up before setting down into a slow descent toward this realm's highest peak. Thor had to admit This part of Midgard did look beautiful from what he could see from up here. The great beast hovered over the top of the peak and there Thor saw him. Tangled within an indestructible tree, was a man who was many things to him, kindly storyteller, braggart, occasional confidant, traitor, and right about so many things.
Both gods jumped off the great beast and landed on the top of the peak. They walked towards the tree, Mimir's Bifrost eyes seem to slightly widen before a fake smile came across his face.
"Well now, look who it is." It was a falsely polite tone Thor knew all too well "The mighty Thor and his wee runt of a brother Baldur. What brings you two here, here to step-in for the so-called All-Father?"
"We are not here for Odin." Thor said it without thinking, Mimir had raised an eyebrow.
"Yeah, I'm tracking a giant. A tattooed man who wields an ax. Do you know of this giant?"
'He's much more than a giant brother, but why does that ax seem familiar?'
"No, I've never heard of such a person. Why? Has Odin's best tracker finally lost his touch, well more than his sense of it?" Hatred appeared in his brother's eyes, and he clenched his fists.
"Baldur." Thor's tone was disproving. "Knock it off."
"Are we going to take this old goat's insults?"
"That's an insult to my goats, nothing but shit comes out of The Smartest Ass Alive's head anyway." Both Baldur and Mimir slightly chuckled.
"Oi that's funny, did ya come up with that while you were sober for once? Although I think your current appearance says otherwise."
"We should go, there's no point in wasting our time here."
"I'll be with you soon."
"Whatever" Baldur just threw his arms up in defeat and walked back towards Dagsetr. Thor looked at Mimir and moved closer.
"Mimir, I need your help."
"Oh so Odin's most 'favorite' lad, actually doesn't think I'm full of it. What would you need help with, grooming yourself, being less of a drunk and a better parent?" Mimir's tone did not change, but Thor almost came to regret this.
"I never needed your help with that, but I need your help to stop Ragnarok."
"So you're doing daddy's work, so maybe he'll show you an ounce of affection?"
"No, he tried to kill me at Ragnarok. I saw war come to my home, to my family." Mimir gave him a look of skepticism to put it lightly.
"Are you drunk, or have you finally lost your bloody mind? Listen to yourself, man. Do you really believe you knocked the serpent through time or that you were as well?" Mimir's gaze turned harsh As for war, what about the wars you and your kin brought to the Giants and Vanir?"
"I never wanted to fight those wars, but I figured I could earn my father's love back. He loved me once, back when-." He couldn't bring himself to say it. He still could remember those old days.
"Father." It was a man who seemed almost like a stranger to him, he was garbed in armor and carried a spear. His face had only one eye and had dark red hair. He had an infant in his arms with a black tuff of hair and brown eyes. [5]
"This is your brother Týr, I know you might not have the same mother, but nothing will ever change that." It was a warm smile, he missed it some days.
"Oh, and now you want to fight back? Where was this spirit when your father sent his forces against Týr. Some 'brother' you are." It was a sharp tongue Thor had no more tolerance for.
"Shut up!" At that moment a storm soon appeared even over the highest peak of Midgard, as furious lightning strikes began to surround the tree. Thor calmed down and the storm just subsided as soon as it arrived.
"Týr was important to me too, I failed him, and I've failed a lot of people. It might as well be the only thing I am aside from a destroyer. But my brother believed I didn't have to fight wars that still haunt me, that I could be more than a killer, and that the nine realms could live in peace. He's right and you were right to oppose my father, but Ragnarok can't be the only outcome can it?"
Mimir could only give him a look of sympathy. "I'm sorry Thor, even If I did believe you, I don't know how to help you. Odin has done his best to scour every bit of prophecy related to Ragnarok and look at what it has led him to do. What if you fall into the same obsessive madness?"
He had a point he couldn't argue with.
"You're right, and I'm sorry I can't do anything for you here. But you were right about both of my sons getting Hrungnir off of me, I wish I believed it sooner."
Mimir felt confused. "I'm truly glad you sound like you've changed."
Thor walked toward Baldur and Dagsetr, but his brother had a concerned look.
"Are you alright? It seems like he really riled you up back there."
"He said something to piss me off.
"And you didn't beat him to death, or try to?"
"He's not worth the effort."
Without a word, Dagsetr started to fly.
"Huginn." Thor dreaded what was going to happen next as his brother called one of their father's ravens.
A cloud of ravens surrounded the dragon and in mere moments they found themselves in Asgard. [6]
I hope I've managed to get the feeling of Baldur and Mimir down, especially with mannerisms for Baldur and dialogue for Mimir, especially a Mimir who has no reason to be friendly to the Aesir.
[1] Odin has a fair deal of sons, and unfortunately throughout all of the various retellings and translations, this list varies with only four confirmed sons across all works. Thor, Baldur, Vidar the silent Norse god and avenger of Odin, and Vali the avenger of Baldur, against Hod.
The other four as written by Snorri Sturluson are Heimdall, Tyr, Bragi the Norse god Poetry, and Hod a warrior god who might be either physically or metaphorically blind who kills Baldur when Loki gives him either a mistletoe spear or arrow. However this can go up to about fifteen and Norse folklore (I feel it would be insulting to call it myth, despite being Catholic IRL) from whatever sources are available, doesn't have a clear capital C Canon. Not that faith or tradition has to have it, but it does mean Odin's sons tend to vary.
So I'm going with Baldur, Bragi, Heimdall, Hod Thor, Tyr, Vali, and Vidar as a comprehensive list of Odin's sons in this universe.
[2] There is a loose God of War timeline for the Norse, and Thor only received Mjolnir roughly 200 years ago before God of War. Maybe he, or at least his sons fought in the Aesir-Vanir war that happened well before it.
[3] In a throwaway bit of dialogue when you first overhear Baldur, Magni, and Modi with Mimir, apparently Baldur came there before asking if his last visit loosened his tongue. Although at the very least two days may have passed while Kratos was in the Light of Alfheim.
[4] Thor has a chariot pulled by Tanngrisnir and Tanngnjóstr, who are goats.
[5] One of Odin's nicknames is Rauðgrani or red beard, so I'm going with a younger Odin having red colored hair, perhaps similar to Thor
[6] I honestly have no idea how Baldur, Magni, or Modi got to Midgard, and I'm not sure how the Bifrost would work in this situation. So I'm using Huginn as something of an out.