After the intro sequence of the Sigil Geode shattering, and the player being introduced to the Hero Paths, a spirit girl known at first only as Guide Spirit, will begin accompanying the player.
After the player completes the quest Something Strange, she will from then on be a follower the player can recruit from dialogue.
The Guide Spirit uses the standard follower system of Skyrim. Players will need to dismiss any base game follower they have and then speak to her to ask her to follow. She will still be able to travel alongside many mod-added companions that add their own management quest to bypass the base-game's single follower limit.
The Guide Spirit has four forms she can take: the initial form as herself, where she acts primarily as a healer, and the three Hero forms unlocked from completing the Hero Paths.
In each form, she'll take on a different voice and use different abilities and equipment. The Hero Spirits can be upgraded to gain additional abilities and improved stats by investing Ectoplasm in their skill trees.
At any time, the player can speak to the Guide Spirit and ask her to change forms. If she is currently taking on the form of one of the Hero Spirits, she'll have an option for the player to return her to her base form: "I want to speak to your true self, become the Guide.".
Regardless of form, after the quest Something Strange there are some common options the Guide Spirit will have when she is not involved in a major quest scene.
Under each form, the player can ask about the Spirit. If in base form, this is "Can I ask you some questions?", otherwise it will be "Tell me about who you are right now.".