Heavenly Day manufactures high-tier weapons, based on fictional life.
Not a lot of people know they exist, which is understandable since they only created a handful of weapons to help with the survival effort. For the few who do know them, many people just dismiss their words. Even then, they distanced themselves from their former name of Hellmass by changing it to Heavenly Metal, before ditching the dark aspect completely and going with Heavenly Day. Rumours are that the company's production capability and quality control ties with K177.
Their name changes are probably related to Hellish Night and their reputation. A statement was released that they aren't associated with them, even with their names being opposites of each other, which may lead some to believe it's some kind of gimmick.