In the interest of compiling for everyone who doesn't have the time and energy to search— all currently known details about HADES II ive managed to absorb, taken from the HADES II faq on the supergiant site (x) as well as the trailer (x)
The protagonist is "Melinoë, the Princess of the Underworld". She is Zagreus' sister, based on another Underworld deity said to be associated with Hades, and she is a witch and sorceress
The shadowed/robed figure that seems to be training her is confirmed to be Hecate via the VA credits in the trailer description— FAQ confirms she will be a central figure as well, as she is a deeply significant figure in many myths and especially pertaining to magic
This game follows the practice of witchcraft, as it is integral to many Greek myths and tales. Their aim is, as with HADES, to be faithful to the sources which inspired them
HADES II is directly confirmed to be a sequel by the FAQ— "[it will be] set in and around the Underworld of Greek myth after the events of the original game."
Their foe seems to be Chronos, the Titan of Time
Though subject to change, according to the list of boons shown in the trailer there seems to be a "sprint" ability and "casts", as well as "magick" (use Magick to fuel casts, perhaps?)
Other confirmed new characters and the titles listed in their dialogue from the trailer:
Moros, Doom Incarnate ("This is an opportunity for you... To make a better future for us all.")
Apollo, God of Light ("Least I can do is light your way down!")
Nemesis, Retribution Incarnate ("About ready to give in?") [Note: melinoë responds with "No. I was born for this."]
Dora, Listless Shade ("You trifle with powers far beyond your comprehension, witch." "...OK if I call you witch like that?")
It seems to be Hecate with the voiceover near the end who says, "Vengeance for your family awaits you."
Hades' words at the end: "He is no mere titan. He is time itself. And time cannot be stopped."
HADES II has been in development bt SGG since early 2021. The early access is not set to be unveiled until sometime in 2023