The latest issue of Weekly Famitsu reveals this is a new playable character who wields two swords at a time.
The magazine also teases that in addition to this character, a cat-eared, silver-haired woman, and black-haired young man (who apparently looks straight out of a Tales of game) are also playable.
It also mentions that the “Nox” in the title “Ys IX: Monstrum Nox” is an important point, and that the concept of “night” will function as an in-game system.
Ys IX: Monstrum Nox is due out for PlayStation 4 in Japan in 2019.
Update 02/27/19 at 11:55 p.m.: Here is another screenshot, via Falcom: