The summary kinda got very long. D: So maybe I will just let you know briefly in my own words, Sabel. Hear me out.
The story that you missed is basically about a masked demon god named Saga who's the son of Queen Hel, a goddess who has lived for several Millennia already. She's kept her son's facial looks concealed, a secret, and that is a major part of the plot in the story.
Saga sorta hated humans when he was a young demon. He grew up wanting to be the best warrior ever. Soon he started craving power, and his mother knew that she would not be able to keep him in check.
Loki, a mad god who steals the treasures of power comes knocking to Tartakus' door seeking for the Tartakuns to join him in his war against Asgard (Heaven) but Queen Hel refuses him and gives him a replica of a treasure of power. Loki is fooled into believing that it is actually the original one, and so he leaves the Tartakuns alone, but not before humiliating Saga in front of all Tartakus.
Because of that humiliation, which his mother let stand, Saga believes his time to leave Tartakus has come. He wants to start anew somewhere else and far from his current home, believing that he's living in shame. He comes up with a plot to take the real treasure of power, but fails in the attempt. His mother tells him that there is another way to obtain true power if that's what he really wants, so she tells him about a dark place and Saga agrees to go there.
In that place, Saga finally falls in love with Ailyth, a human maiden he hated for so long. He comes close to losing her, and that changes his evil ways too much. But then, two demons who Saga considered as his best friends, die in Midgard, (this after Saga released them) and Saga is angered beyond reason. Soon, he comes to the land of Midgard where humans and other short-life span creatures reside. That is where I left off. Truly, you ought to read the first one so you can understand better, I am terrible at telling someone what happened. Really, there's many things I left out that have to do with the story, so I recommend you read it, I promise you won't be disappointed.
Have you read the new one?