Astrid stared dumbfoundedly at the scene. Despite Hati's warning, she still caught herself wondering where that domineering Master character from before suddenly disappeared to.
Luckily, she quickly recovered and gave Sif a bow while saying, "It is an honour to meet you, Lady Sif." Sif cocked an eyebrow in response and said, "Lady? Am I not your mistress?"
Barely managing to keep a straight expression, trusting that Hati wouldn't let anything happen to her, she answered, "Please forgive me, Lady Sif, but am I your maid or Master Hati's?" while thinking, 'When did I already start trusting him to keep me safe?'
Hearing this, Sif started giggling and said while smiling, "Oh? Aren't you the brave one? It seems you have taken a shine to my Little Hati. I wonder if that has anything to do with my brother's little prank." Hearing this, Astrid's face started heating up.
When Sif noticed this, she smirked before continuing, "But this is fine, too. You are indeed little Hati's maid. As long as you serve him faithfully, you can call me whatever you like, within reason. But remember…"
At this point, she waved a hand, causing Hati to suddenly lose his hearing, before she continued in a grave voice while unleashing some of her bloodlust, "If you harm Hati in any way, I will rip you apart from the seams." She knew Astrid wouldn't be able to harm Hati directly because of the blood seal, but there were always other ways.
Astrid, who felt as if she was drowning in a sea of blood, quickly nodded her head with an expression as if she just saw her worst nightmare, meanwhile thinking, 'Fucking hell, as if I needed more reason not to betray Master, he also has a homicidal mother.'
Then, as soon as the feeling appeared, it also disappeared again. She was sweating and unstable, but she was still on her feet. Something that impressed Sif, as most people her age would have at least fallen off their feet.
While hearing none of this, Hati could more or less guess what just happened based on context and Astrid's expression, causing him to get a whole new appreciation for his mother.
This was also another proof that people in this world have some sort of powers like he and Luna have. Combined with the blood seal Leif mentioned earlier, he figured it was time to learn more about this, so he asked Sif, "Mother? Why could I not hear anything just now?"
Sif, always surprised at Hati's naturally calm disposition, looked at him and smiled gently, "I just used my control over the element of wind to block your ears, honey." Hati, putting up a surprised expression, responded, "Eh? You can do that, mother? That's awesome! Is it like that blood seal thing Uncle Leif talked about? Can I do that, too?!"
Sif chuckled at his enthusiasm and responded, "Maybe, but you'll need to incorporate the element of wind in one of your three focal points." Seeing Hati look at her with a confused expression, she said, "Well, maybe it's time to tell you about the path of Asgard's Einherjar."
She then looked at Astrid and adorned a stern expression before saying, "I will now spend some time teaching my son. You can make us some tea and then get acquainted with your real room, which is connected to your Master's. You should be able to find it."
Astrid shot a quick look at Hati, and seeing him nod, she started to move towards the tea set in the corner.[1] Sif was a little surprised at this interaction but inwardly approved. Hati then said, "Mother, do you mind if big sister Astrid stays for the lesson? It would be nice to have a study buddy."
Hearing this, Sif shot a look at Astrid, wondering if she was the one who asked for this. But in the end, she decided it was fine either way. If Hati wanted his maid to be more knowledgeable, then she would indulge him. So, after Astrid returned with the tea and was told she could take a seat, Sif started teaching them about Asgards Einherjar.
Einherjar use techniques to absorb energy into the body's focal points and then use that energy to grow more powerful. Energy can also be absorbed without a technique, but this is so slow that most mortals without a technique don't step past the first revolution.
Of course, theoretically, a learned mortal could create his own technique. Still, without getting inspiration from existing techniques that went through thousands of years of progress, a self-created technique is likely not much better than natural absorption.
And because techniques are tightly controlled, it was rare for someone with mortal parents to pass the first revolution.
Any humanoid race in Asgard has three focal points in their body, while beasts have their own thing going on. The three focal points are the soul core, the heart and the spirit core. The heart is considered the main focal point, as the soul and spirit core are tightly connected to and even created from it.
Every focal point has nine stages before every revolution. They can progress through these stages by absorbing energy into the appropriate focal point. A mortal who starts on the path of an Einherjar for the first time will first need to raise their heart focal point to stage nine.
At this stage, the heart will create the soul and spirit core, which then settle in the forehead and the lower abdomen, respectively.
The three focal points have a clear division of labour in operating an Einherjar's body. The heart represents everything physical, from muscles to blood to bones. This is also why the heart needs to be raised to stage nine before the other two focal points are created, as the body needs to be powerful enough to carry those systems.
The spirit core represents the energy generator of the body. When fighting, the spirit core generates energy and provides it to the heart and soul, as mere absorption from the surroundings would be insufficient during battle.
Meanwhile, the soul core naturally houses the Einherjar's soul and is responsible for controlling both the body and the spirit energy from the spirit core.
Because the three focal points have such a symbiotic relationship, losing any one of these focal points is essentially the end of your career as an Einherjar. In fact, the only Einherjar that have lost one of these points and are still walking around are those that lost their spirit core.
After all, the spirit core is only responsible for extra energy during combat, but as long as an Einherjar with no spirit core avoids combat, they can continue to live. The same does not go for the other two focal points. Obviously, the heart and soul are essential requirements for life.
But besides that, a body without the heart focal point would simply collapse under the weight of the soul and spirit core, while an Einherjar without the control provided by a soul core would simply explode from their energy going berserk.
Because the three focal points are so interconnected, the only way for an Einherjar to undergo a revolution and rise in power is for all three focal points to be at rank nine, at which point the soul and spirit core will be sucked back into the heart to undergo restructuring.
Although it is technically possible to keep raising a focal point rank beyond nine, this is essentially considered crippling yourself, as revolution becomes impossible, even if you bring your other focal points to the same rank afterwards. There are rumours about methods to solve this issue, but they are rare and far between.
Generally, going beyond rank nine is only done by those people who have reached their ceiling in one focal point and are unlikely to be able to go through another revolution before old age claims them.
From zero to six, every revolution came with its own title. These names are, respectively, mortal, grunt, warrior, ace, paragon, master and grandmaster. Each revolution came with a rise in strength and status while also granting various other benefits, including an increased life span.
Every revolution, starting from the second, essentially doubles an Einherjar's lifespan, from a mortal's lifespan of 100 years to a grandmaster's lifespan of 3200 years. This means the first revolution does not increase lifespan, presumably because all the extra lifeforce goes into creating the soul and spirit cores.
Hearing all this, Hati was genuinely shocked. He knew this world was different from Earth, but only now did he realise exactly how different. He also realised that his and Luna's abilities on Earth differed from what his mother was talking about.
After all, he certainly never absorbed any energy that he was aware of. It seems he would have to do his own research on this because he obviously couldn't ask his mother about it.
[1] Fun fact: Vikings drank tea, too! Though it was more like an energy drink, and I doubt they had libraries with tea sets.