Lore of Dark Winter

120 Years ago, there was a war, between mortal and fey creatures over a disturbance in the planescape, the feys thought their magic was being sucked away by the mortals, and the mortals thought they were overflowing the mortal plane with magic to make it their feywild.

Both sides were wrong, proven as the void shattered reality. With a last ditch effort to fight said void off, the heroes of the time perished. The world began to shatter, air would disappear, the void grew stronger.
In the end, only some very capable beings and the powers of nature were left on a single island, with ever so slowly dwindling resources.
Trying to fight back the void, the powers of Spring and Winter have vanished with multiple other capable warriors of the time, only to leave aftershadows of themselves to haunt this now dark realm.
The power of Fall and the nowadays referred to Goddess of Ice Miyuki put their last effort into creating new life on said island they resided in, making it the only place of the living nowadays.
The power of Summer is the one that remains, as a creature that has sworn itself to protect the sacrifice of the Ice Goddess and the warrior of Fall.

Skip forward 120 years into the future.
Everything is dark, with no day or night. There are floating islands that people travel with the help of moving rocks that seemingly don't change trajectory too often.
There's only one safe spot in the entire world, and it's protected by one fragile sphere in the middle of all of it. Here is where two powerful mages put all their effort into to keep this place alive, with one person declaring it her sworn duty to protect said sphere till the end of their life.
Outside of Safe Haven there are only shadow creatures; strong, powerful beings the void has devoured all those years ago, spat out as a now living creature of their realm.
Two of these are the Winter Void and Spring Void, both appearing at their respective seasons, with the Spring Void being signified by the dark poisonous flowers growing stronger than before and sucking the life out of people even within Safe Haven.
And the Winter Void, the topic of today's hunt appearing around the winter time, causing heavy snow storms, people freezing to death without the protection of the sun, crops dying and winter demons crawling out from hiding.

You guys have gathered to put an end to the Winter Void, may it be for the coin, for the safety of a family, for your own personal hunting achievement, it does not matter. You brave warriors have decided to put an end to the once legendary warrior now turned shadowy mess.