Zefir is responsible for the fantasy part in the series. What exactly is Zefir? It would be a mistake to call him an alive human being. Zefir comes from a completely different realm, the alternative/real/ world, basically from our medieval times. It's the same Zefir as HERE, with the same past story - he once used to be a human (halcylian from Halmaime Island), a powerful inventor who accidentally casted a kind of curse on himself and trapped part of him behind the universe for hundred years. In the RS series it turns out that Zefir gets an alternative version of his story AFTER he gets released; both versions from both series can be considered canon if we accept alternative universe theory.
In RS Zefir is a mysterious spirit who seems to be aware that he got released in a different dimension that he belongs to, but he has no other choice than use his chance to finally "get out" and disappear forever. He is still trapped in some kind of weird matter that doesn't let him truly enter the world and keeps him "alive" at the same time, and it's not possible for him to get rid of it. In the exact moment when Zefir appeared in this dimension, he somehow "implanted" himself in a first random person who also appeared there at the same time, who turned out to be freshly born Armin. Zefir needs a fuel to exist and keep destroying the matter around him, and this fuel is Armin himself. _{Yes, he literally needs to exist if he wants to stop existing, there's a lot of magical shit to explain.} In that sense Zefir is some kind of parasite, but the bond with him has many weird results, as Zefir is just... wild unclassified intergalactical being who doesn't even control what's going on with him. Zefir needs Armin's emotions and the emotions he causes in others, believing it "melt" the alhi-parts on him. Their bond is actually very complicated and it gets more and more dangerous with time, it has an impact not only on Armin himself, but it starts to "infect" the world too. At the beginning Zefir seemed to not care about Armin at all, as he was basically unable to feel any own emotions, but after years, due to Armin's impact, he became more "human-like" and eventually started to develop some actual emotional bond with Armin. Zefir in fact influences his mind a bit and unconsciously making him experience weird unreal things or see things that shouldn't be seen. It is not possible to completely separate them, but Armin attempts to do it, when he gets extremely angry at Zefir (after discovering Zefir had something to do with Audrey's death). It turns out that it's enough to release Zefir from the alhi-parts, what results in Zefir's actual appearing in visible form. Zefir and the matter he's made of still keep evolving somehow - and it seems like it destroys him slowly. And while Zefir, tired by his 800 years of existence in very poor form, truly wanted to be destroyed, in this moment he's not so sure about it, because he is aware that it will destroy Armin too. Surprisingly, to protect his host, Zefir learns to control that substance and somehow REVERSES it's feature, making it working completely different - now it doesn't destroy him, it makes him grow stronger... but also losing his consciousness, and, what's worst, turns him into super powerful being who doesn't control his actions at all. Zefir is on a straight way to reach his final form, which turns out to be dangerous for the whole world. Zefir is not just one specific dangerous being, Zefir is everywhere. That's why Armin is like oh mai, I created a monster.

- When Zefir appears on Singya, Armin is still angry at him, but he knows he can't just simply let him go without any supervision, as he doesn't know WHAT Zefir actually is now, so he has to keep him around himself. That's why Zefir in his first stage of new existence becomes Armin's pet. This version of Zefir is silly, seems innocent, keeps apologizing to Armin for using him for so long, tries to enjoy this version of life and willingly explores the new dimension. Zefir is totally obedient to Armin and at some point he even wishes to have a normal friend relationship with him, forget about the 800 years of floating in space and have some fun. In this form he's not really dangerous to anyone, but it changes with time.
- It is impossible to touch Zefir, he looks like a human being, but he has no actual body.
- At the beginning Zefir is scared of new technologies, but is also very curious about them,
- Zefir even sleeps in one bed with Armin's dog Luxemburg.
- In this stage Zefir is noticeably worried about Armin and don't want anything bad happen to him.
- Zefir wants to use social media. He can be found on Facebook already, look for Zefir Triangle Kowalski.
- A lot of Armin's mates don't believe in the fairytale about 800 years old interstellar parasite and just think that Armin brought a new weird friend from other country.
- Armin and Zefir are somehow bonded even after Zefir gets released and appear in person, but after this, Zefir doesn't have access to Armin's mind anymore, and this particular moment of their semi-separation is actually unbelieveably exhausting for Armin himself.
- Zefir dislikes electronic music, he prefers metal.
- Zefir is the End of the World.