Not exactly. This is not a sequel to or related to the Killer 7 world in a any way, but it does continue Sudas tradition of "assassin protagonist" games. Killer 7 was godly, but the rest of his work has been hit or miss for me, so I'll watch this closely to see if it merits a purchase.
Since it's a Suda51 production, I'm gonna say you can play this game after having indeed played Killer7 and still not fully understand it, haha. But, yeah, it shares no canonical ties with Killer7 so you'll be alright. However, I do recommend you play it at some point!
I'm concerned. X-Seed isn't exactly known for great QC - they pretty much just publish whatever is handed to them. I remember way back when their Wild Arms titles (specifically Alter Code: F and Wild Arms 4) were just glitchy monstrosities