Or at the very least, related to the Tales of Zestiria the X anime.
This rumor, though not that widespread, has been floating around ever since Tales of Berseria and the Tales of Zestiria the X anime (formerly named Tales of 20th Anniversary Animation) was first announced. Specifically, a particular symbol on the back of that new character shown in the original Tales of Zestiria the X trailer was also seen on a town banner in some screenshots or scans of Tales of Berseria:
Back then, it wasn't concrete yet if there was a connection between the two, as some defended that the "Tales of 20th Anniversary Animation" might not only be about Zestiria, given its name. Now that it's been now renamed as Tales of Zestiria the X, it seems to be leaning more toward some sort of connection between the two games.
Cue in the new Tales of Berseria trailer. Some things in the trailer have caught fans' eyes. Specifically, the following:
Speaking of the said knight, some find the two men accompanying him to be similar in design to what we know was some of the Seraphim in Tales of Zestiria, specifically the ones that are in the trials. Actually related? Or just some sort of model recycling?
The following assumptions made by fans may seem far fetched to some, but they've been raised multiple times so I thought I'd add them in:
^Or that Lifiset is a seraphim mainly because he seems to wield seraphic artes and that the ends/tips of his hair is a different color (though I think this is better confirmed with art from ufotable). The latest news from Shonen Jump states Lifiset as a "spirit" though. In Berseria's world, spirits are apparently used as slaves. With that said, they're probably entities people can see, so that sort of crosses this out by a tiny bit.
Note that all the points we raised above are just mere rumors for now and is not official news. Is it true? Only time will tell. For now, let's have fun with the speculation embargo.