Certain characters in the game only appear (or are mentioned) if certain conditions are met. This article contains DETAILED SPOILERS.
Ignatius, Duke-Consort of Mead, will appear only under two conditions. If Julianna is imprisoned, he will appear at the palace to resolve the rulership of Ursul. If you make him Duke of Ursul, he may then appear at the Grand Ball if a vote of no confidence takes place. Otherwise he will only be mentioned, not by name.
Fabian, the Earl of Titan, appears if Divination skill was used to read an omen prior to the Grand Ball. He will also cast a vote as regent of Elath if the vote of no confidence takes place. Otherwise he is only mentioned by name.
Arisse, Duchess of Lillah, may appear if a vote of no confidence or a civil war take place. Otherwise she is usually mentioned by name in discussions to do with Elath. She will also appear if Elodie negotiates an end to the civil war.
Talarist of Sedna will only appear if his gift is accepted. Otherwise he is only mentioned.
Selene only appears if Julianna's mentorship was rejected in some way, or if she is needed to handle the cleanup after the Lumen conjunction with the fleet. Otherwise she may be mentioned if you study Lumen skills and attend the chapel.
Several nobles will only appear during the vote of no confidence at the Grand Ball: Severin and Armand, and if Hellas has changed hands, Bennett. Bennett can also appear at Gwenelle's party if he has received a title by displacing Banion or Brin.
Evrard only appears if you've taken Julianna as your Mentor and pass a Climbing skill check when you spot a possible thief.
Adair only appears if you choose to dance with him at the ball or become engaged to him after his father's death. Otherwise, he is mentioned by name when discussing the succession of Elath.
Several members of the Elath family will only be mentioned if dialogue with Fabian is unlocked, otherwise they're only mentioned in Intrigue skill text.
Arisse's son, Thaddeus, will only be mentioned if a peace is negotiated instead of civil war.
Arisse's son Kiran is mentioned when questions of inheritance of Elath or Lillah come up.