When the game was announced for Steam, additional content was also announced. This content does not appear in the original version of the game, but anyone who bought the game in direct sale can get the expansion, either directly or by receiving a Steam key through hanakogames.com.
New characters
The characters of Alice and Evrard were added to the expansion. Alice appears throughout the game in the role of the previously unnamed maid, but has several unique encounters and her own special ending. Evrard appears conditionally. He also has several unique encounters, and several possible endings based on how well events turn out. Alice and Evrard are siblings.
New dialogue
there is quite a lot of new dialogue. Charlotte makes several additional appearances under certain conditions. Julianna may be questioned further about Lumen lore. Brin has a conditional encounter with added dialogue and backstory.
New storylines
There are several new storylines. If Julianna is imprisoned during her first appearance, this unlocks several possible story paths, which lead to several different achievements.
New skill checks
Several of the skills which were rarely useful have additional skill checks which are meant to make them more worthwhile. This includes falconry, climbing, and several others.