I've received information that the sprite is labeled as "4_M_ROKI" by the developers. And the filename for the illustration was "tnm_loki," so it most certainly isn't Thanatos. I assumed that the instance was just using Loki's sprite as a stand-in for Thanatos, but I see now that wasn't the case. Considering how Loki's dagger is called "Sword of Shadows," it's likely that his mystery name of "Magic Swordsman" is a reference to that. I thought it was rather weird that Thanatos would accompany the Assassin Guild group instead of Loki, but the video confirms that it's Loki that came with them and not Thanatos. I'll correct the pages to reflect this.
Thanks, sorry for my mistake. Since Loki doesn't appear during the battle against Surt at the Thanatos Tower (only during the battle against the evil fanatic) I thought that would be Thanatos in disguise.
And also due to the time that the event occurred, but I always forgot that Loki isn't a normal Norman and Julianna Lucille that is alive today was there too.
I think all of that would've been cleared up in Volume 11 of the manhwa since Volume 10 ended with the fight between Loki and Julianna just starting. Somehow I doubt that'll be elaborated on in RO, which would be really sad. I hope the story gets to us one way or another, but I've heard Lee Myung-jin hasn't been dedicating as much time to RO these days.