Well well, what do you know? I've decided to make another mini-shrine for one of my faves. At first, I decided against doing anything Loki related because everyone knows he's my favourite Granblue Fantasy character and I've talked about him countless times. But then I realised... It would be far, far more helpful to just drop all my rambling about Loki in one place. So here I am.
Loki is very personal to me because I relate to him a lot. It's probably why I have such a good grasp on his character. Looking at him is like I'm looking into a mirror. He is very, very deep... but he's easy to understand once you get to know him. I hope to help others enjoy his character a little bit more with this shrine!!!
You're in for a lot, but I will try to make it easily digestible. Are you ready?

Astrals are a race in the world of Granblue Fantasy, they are best known for invading the Sky Realm and causing a war between the stars and the sky, with the Astrals representing the stars, of course!
They are noted to be immortal and stagnant in terms of growth (psychologically and physically) - while Skydwellers are able to evolve both as individuals and as a civilization. It has, however, been implied that if an Astral remains in the Sky Realm and accepts the laws of it, they too can change, even though they're not supposed to be able to. One example of this is Loki's brother Byleistr, who was able to form bonds with many Skydwellers and even have a child with his wife. Byleistr managed to lose his immortality and die in an accident, which left Loki quite shaken. More on this later though.
Astrals are the ones responsible for the creation of Primal Beasts. Their knowledge of magic and technological advances are at a much further point when compared to the Sky Realm. A normal Skydweller should not be able to stand up to an Astral... And even Primal Beasts - despite how strong they are - cannot resist the pull of an Astral. It is safe to say Astrals are the Omnipotent's idea of a perfect entity.

Loki though? He's far from the perfect example of an Astral. He's considered an outsider and loner, and nearly every Astral that meets him makes it clear that they hate him. The reason for this is interesting... Loki enjoys being an eccentric person and he's somewhat of a bastard (literally and figuratively). The details surrounding his upbringing are mostly unknown, we just know that he is of low-birth and had rough time when compared to Byleistr who was the prime example of what an Astral should be. Personally I headcanon that he is an illegitimate child. It just makes sense to me.
Despite all that, Loki is still extremely powerful and can do whatever he wants whenever he wishes. Other Astrals have grown to fear his magic, as it is so intense that it's considered wrong... Even when the main character and their crew had been through countless battles, they found themselves unable to fight Loki and he completely overpowered them.
So Loki is pretty cool! Pun intended because all of his powers are ice based. He's full of whimsy and extremely free spirited. While early MSQ portrays him a bit different than how he is now, it was plain to see the idea that Cygames had in mind for his character. He's not evil and I'd argue that he's not even an antagonist, he's more of a mischief maker. Basically I can summarise him in two images, which are the following:

Let's start at the very beginning. Loki was first introduced in an event called Winter Nights, Stardust Memories. He was portrayed as a complete freak who wanted to take away Lyria, Vyrn, and Rosetta from the captain. He claimed that he could take better care of the Girl in Blue and the Little Red Dragon for reasons that are unknown... I would sum it up to him being a menace and trying to cause a big scene that gave the crew a certain idea about him. He treats Fenrir very poorly in this event (as if she were his pet basically) which sucks but thankfully this event is not considered to be canon and he got a proper introduction in MSQ a bit later!!
His real introduction has him break into the captain's house and that's how he meets the crew. I assume he just was chilling there until he was discovered, which is very funny to think about. Orchis is there when the crew meets him, and it is then that we discover that she is his niece! He then proudly declares that he is an Astral and the last one left in the sky at that. It's hard to believe, but it is in fact true... Just as soon as he appears, he takes his leave and returns to the Erste Empire to cause issues for his high ranking officials.
To back up, Byleistr (his older brother) was the previous king of the Erste Kingdom. To Loki, this makes him feel like he has a right to the throne, so he declares himself the emperor and causes chaos. He doesn't really do much of anything as the emperor, as most things were handled by Freesia, but it's something that seems to be important to him. His connections with Erste are very strong and he is still considered a part of the Erste Royal Family.
In Act 1, he is encountered here and there and up to no good. Or at least... that's how he wants it to appear. The truth is that everything he does to get in the crew's way actually helps them. It's strange... For someone who is supposed to be a sadistic person, he doesn't fit the description. This is further amplified when we see him have a breakdown over the fact that his brother is dead.

Oh, I don't know. Maybe I just don't care about anything anymore.
It's been this way for a long time. No matter what I do, it's just not as fun as it was before.
Every time I wonder why, I come to the same conclusion.
And you know what? I think it'll take something like Akasha to alleviate my boredom.
Perhaps we should have used it sooner. It doesn't matter what it would have done—so long as everything disappeared.
Then I wouldn't have to feel this way now. It's all just so... stupid.
Why... Why did my brother...

This is the first glimpse we get into what lies beyond Loki's icy eyes. It's clear there's more to him than someone who just wants to hurt and betray, and that perhaps... the whole thing is just an act... Loki seems to be self sabotaging himself over everything that happened... But the player can't help but wonder if this really is the case. Loki likes being mysterious and doesn't like letting people know what goes on in his head.

Loki has a sparse appearance in Act 2. He shows up without the crew knowing and forces a Primal Beast to give them a piece of the Sky Map. Despite the fact that the Primal attacked the crew, it turns out everything was for their benefit... even when Loki threw them into an entirely different Skydom, that too aided them. Loki may have been meddling, but he wasn't causing issues in the long run. Far from it.

Act 3 is where most of his character development occurs... the segment is named after him too! Wayfaring Astral does indeed refer to Loki. It is here that we see he respects Fenrir but doesn't know how to admit it. The two share an unbreakable bond and he even managed to reach a true understanding with her that allowed Fenrir to release her full power with his help. Fenrir doesn't take crap from Loki when he acts like a little freak, but she's extremely loyal to him and just wants to help him find what he is looking for... To help him remove his inner mask. It's obvious to the viewer that the two care for each other but their own individual struggles prevent them from being clear about it.
Loki has shown significant change in Act 3, which shouldn't be possible for an Astral. He is accepting the Sky Realm's way of life and becoming a part of it just like his brother did. Everything he does is because he wants to understand the world in the way Byleistr and the captain do. He's still on a different axis than mortals though, so the way he views the Sky Realm will always be a little off, but nonetheless everything he sees is reflected back into him. He is an observer to everything, but he knows that one day soon it will be time for him to take the stage. Fenrir even gives him a pep talk and explains that he doesn't have to be afraid of forming and losing bonds. If he really wants to be serious about all of his goals, then he needs to conquer his fears about everything... He does indeed take this advice to heart. The first example of it is when he saves Zwei from despair and offers a helping hand to her. His past self would have let things play out but this time he actually involved himself... and he continues to do so.
It doesn't come easily. Loki still has a ton of baggage and doesn't know how to tackle it yet. But he continues helping the crew in small ways. He starts his own journey with his very own crew that follows in the captain's footsteps. And eventually... he reaches the conclusion he sought. He might not know how to feel about it, but he realises a lot of things. And thus he joins the captain hand-in-hand and sets off to Estalucia with them. What awaits them there is unknown, but Loki thinks that'll be interesting, and he wouldn't want it to be any different. The stranger something is, the more exciting it is for him.

Yeah, sorry. That was mean of me.
Your eyes were just so bright and innocent that I felt the need to tease you a bit.
Acting a little more like his old self, Loki takes Gran's hand.
Unorthodox is just the way we like it.
Let's do whatever it takes to get there. To the place where every wish is granted—the Holy Seat of Genesis, Estalucia.

Loki is a fascinating character and I've really only covered the basics... I'd like to touch up upon his relationships and highlight some of my favourites. Even if he thinks he is incapable of forming bonds, this is not true and he is lying to himself due to his issues.

Gran/Djeeta

Loki's relationship with the captain is so peak to me. Loki is a direct foil to them and that kind of bond in media is something I really adore. It might not be obvious at first that Loki is intended to be their foil but after his journey and actions it's something he deserves!
Loki forms his own crew, goes on his own journey, learns about himself and others, and of course, changes the skies for the better! He'd probably never admit that he's a good person, due to his trauma and the like, but he is. He was never evil. He fought against evil if anything. I didn't touch on it, but he despises the way Astrals treat Primal Beasts, especially the reseachers that torture and manipulate them. While it might be normal for the other Astrals to treat their creations poorly, he actively stood against that and even rescued Fenrir from certain death. This will to save others of your own volition even if it goes against everything you know... that's something so special that Loki and the captain share.
Of course, Loki did toy with the captain at some points... their relationship isn't perfect... but he changed due to them and now his intentions are pure. The captain too, changed because of Loki even if it was far more indirect. His subtle nudges to point them in the right direction had a very real impact. Loki has also saved the captain on multiple occasions, whether it be against the Otherworld or preventing the captain from being erased from reality, Loki has been there to help when they most needed someone.
Loki wished so desperately to understand the captain and he's now at a point where he does understand them. He's even on a journey with them to Estalucia! I'll be honest, that was what I was hoping would happen for years because I saw all the hints Cygames was throwing out... Now all that is left is for them to release Grand Loki! Come on Cygames!!

Fenrir

Oh good heavens where do I begin with these two. Fun fact: Fenrir is Loki's child in Norse mythology. Now you know. I personally view them in a familial sense because of this but you do you.

Loki treats Fenrir really poorly at first, or at least, that's how it appears. She, being the ferocious Primal that she is, never takes it sitting down. She's not afraid to talk back to Loki and call him out. This is a good sign though, because it shows she isn't fearful of him. It's her way of showing she cares for him. Even with Loki's weird pet jokes, it's clear there's something going on with him too. He might brush off Fenrir's concerns, but he also shows his vulnerable side to her multiple times. Fenrir may not know what to do in situations where Loki shows how deeply hurt he is, but she does know that she'd do anything for him and she refuses to leave his side.

The truth of everything is revealed in late MSQ but also surprisingly, a side story known as Ranger Sign Bravo. Both tell us a similar story about how Loki rescued Fenrir from a Primal research facility and how her chains are actually to limit her powers. Should she lose her chains, she would unleash her true strength and die since she was considered a failure of a Primal Beast. Loki being the misfit that he is, didn't care about that though and instead gave her a purpose for living.
I love their bond so much. Fenrir is so amazing. I miss her. MSQ is brutal and the fact that Loki mourns over her says enough.

Byleistr

Yeah we all saw this coming. It's him, the guy who is only mentioned 4-5 times in all of Granblue Fantasy and haunts the narrative because he's been dead for ten years. Loki has mixed feelings towards his older brother. He didn't approve of him falling in love with Viola and the Erste Kingdom. Loki was extremely bitter over it and began to hate everything Byleistr touched (namely Orchis, his niece AKA Byleistr's daughter).
But that wasn't the truth. Loki was extremely damaged by his brother's death. It's not stated outright, but the two had to have been close. Byleistr was an extremely kind person and would have been receptive to Loki's situation (remember, he's of low-birth). I have no doubt that Byleistr often helped Loki cope with it all. So losing his only family member that genuinely cared for him must have stung. It's to the point where Loki says the world is boring without his brother and that nothing is the same without him. Loki might try to act apathetic but he really isn't.
Loki also desperately wishes to see the world through his brother's eyes. To me, this means he viewed Byleistr as a role model, which again, shows he did care for him and is just hiding his true feelings about everything.
May we get Byleistr flashbacks soon. I need to see him so badly.
Throwing one last fun fact at you, but Byleistr is how we know Loki's last name is Arcus. He is referred to by his full name, Byleistr Arcus and we can assume Loki has the same last name. Probably. To me at least. Arcus is a type of storm cloud, which is extremely fitting given the meaning of Byleistr's name (surprise surprise! It has to do with storms). The Loki of Norse mythology also has some stormy associations (lightning, to be specific!) so... I think it all checks out! There is one issue, which is that they actually mispell Arcus as Arqus for... some reason? No way to really know which one is right but Arcus has been used more and it just makes more sense to me given everything. Oh wellsies!