I'm not sure if anyone has heard of this manga, as I found this monthly manga from my brother called Shuumatsu no Valkyrie: Record of Ragnarok. It's a monthly Seinen manga in which 13 Gods from various mythologies and 13 historical humans who are aided by the 13 Valkyries battle it out in 1 on 1 matches to determine the fate of humanity in Ragnarok. In a sense it's a what if you did a battle tournament arc for an entire series.
As I am posting this thread currently 39 chapters are out though the 40th may come out this month. So far there have been 4 concluded fights with the 5th one appearing to be wrapping up soon. From what I have seen most who have read the series enjoy the 2nd and 4th fights the most. I won't spoil any of the outcomes of the fights, but will say they have been some of the best I have ever seen, especially in the suspense and tensions.
It is written by Shinya Umemura & Takumi Fukui (This is the first manga I have seen to be written by two people at the same time and illustrated by Ajichika. There are 9 volumes out, but I don't think they have been published in English yet, so you would have to search it online if you want to check the series out.
Here is an image of the first volume, to get an ideal of the art style