Cover is great, synopsis is fine / average. Not sure how I'd improve it.
I guess we got told a lot of information about the past / character background (The arson, 3 years of isolation, an angel forcing him to save people even though he doesn't care about it, he's a devil...). But I still don't know what the story will really be about aside from "He is chosen as 1 of 6 Heroes to save the world." It's still kinda vague and unspecific, it's not clear what to expect, if that makes sense. We got a lot of facts, but didn't get a feel for the MC's character or personality. Or from where the "fun" will come from - the genre is a bit unclear.
(I don't even know if these "heroes" are in the modern world unless I see 1 of the 30 tags saying "Modern fantasy", at first I thought it was more like normal medival fantasy, oops!)
I skimmed over the start of the story and it takes 8 chapters to even reach the point of "new" stuff happening that wasn't covered in the synopsis. That is also unusual if you ask me. Because for those 8 chapters the reader kinda already knows it all (since it was in the synopsis), and is paitently waiting for the story to "start".
I think it's more usual for the first 1 or 2 chapters to "escape" what was said in the synopsis and continue with the story.
Not sure if any of this made sense or is helpful, I'm just trying to give random ideas. Many stories on SH also often like a more "informal" style of synopsis, like this:
So, let me get this straight, I die not knowing how, get reborn as a mythical bird, my parents are dragons and this levelling system is crap. If that isn't bad enough, I'm also terrified of flying. I'm never going to get used to this, am I? ---Slight summary of...
www.scribblehub.com
I think it's a sweet and effective blurb, immediately shows the tone and the personality of the MC, and it's clear what the story will be like. It's maybe not applicable to your story bcs of the vastly different genres, but I wanted to mention it as contrast.
There is also alot of stories like this one where in the synopsis the writer talks to the audience directly and describes what the story will have and won't have, trying to "sell" it to the audience and adjust their expectations in advance. This one is super long and idk if any readers would ever read it all, but it's also a relatively popular approach:
Synopsis John was just an average, everyday old man. He had always worked hard, had a wife, kids, and family. He had lived what most would call a good life. Then one day, at a crosswalk, some kids were not paying attention and tried to cross. A truck was barreling...
www.scribblehub.com
Good luck, maybe some adjustments could help it attract more readers, the writing is pretty good!