Tertia

The dwarven goddess, sort of. She is very mysterious at present, and the dwarves variously believe that she has died, abandoned them, or entered some kind of seclusion. Supposedly they do not worship her.

Tertia is mentioned by dwarven characters throughout the game. In particular, a dwarf at a shrine in upper Eustrin mentions that the party is free to worship whomever they wish at the shrine, and that "Tertia did not preach jealousy." The same dwarf says Tertia was goddess of "all the Earth, not just the rock" and implies that she should not be considered just a goddess of dwarves (that is confirmed later).

Story
During a visit to Eustrin (chapter 5), the party finally meets her, but she is not what they were expecting.

She is an old, really old entity (she describes herself as the "I am the goddess of the world itself"), but she remembers later that she wasn't present at the start (she can't even say if there was ever a truly beginning). That means that she has forgotten quite a bit of her own story (that includes her own origin, as she doesn't recall if she was mortal once or not). Taking that into account, she is able to fill some blanks about the Goddesses, the Incubus Kings and the relation between the shards (but it takes a while as she is weary, tired, and wish to be left alone).

After discussing alternatives, Simon takes Tertia sexually, and in doing so draws her power under his, to an extent. The party mages also detach Tertia's garden home from its location at a far end of the Tower, and connect it to their Headquarters via the magic lab.

Relationship points
Base value: 20 Maximum legit value: 37 (Tertia is unlikely to be maxed.)
 * refusing the opportunity to whore Qum, OR whoring Qum.
 * funding representation for dwarven interests in Ardoheim.
 * investing in Eustrin Guild of Blacksmiths before Chapter 5. (Only available if you convinced them to allow outside investment.)
 * funding cleanup of Gasm Falls water before Chapter 5.
 * securing major support for Tak'Kan corruption cleanup at Council of Gawnfall, OR minor support.
 * copying Reletima.
 * if Tanurak didn't affect Erosia, OR if Tanurak affected Tak'Kan.
 * visiting all 8 points of interest in Eustrin with Neranda, OR visiting 5.
 * exterminating the Dwaregasts in Deep Tunnels on the first visit to Eustrin in Chapter 5, OR later.
 *  Liberating Eustrin from Aram's control
 * Tertia Induction sex scene. (Speak to her in Garden of Earth with 30 affection, after attaching it to HQ.)

Scenes

 * Tertia Titfuck - Simon and Tertia start to explore how their relationship should work. Unmissable.
 * Tertia Induction - Simon and Tetria carry on forging their link. This involves hotdogging while Yarra watches and masturbates with her tail. Tertia in Garden of Earth with 30 affection.