Hi there,
Spoiler
In order to get to stay as the Transient One, you need to be on Jeth's route, have his pendant and bond 6.
When you have the dream from the gods answer the following:
"No, it's not fair!"
"I want to return to the simulation."
"Don't care. Send me back."
"No, let me resume."
In order to keep your VP low and get the "kidnapped" ending you have to side with Brookhaven WITHOUT romancing anyone. Try to choose all benevolent options and politely refuse any romantic advances from any of the characters. If your VP is 10 or less, the night before the war departure, you will overcome your drowsiness and catch watermage before he leaves.
"Where are you going?"
"Wait... Take me with you!"
"I want to help the Great Seer."
Watermage will get scholar Beileph and the three of you will plan your escape the next day when the carriages are leaving for Brookhaven.
Much of the war goes the same as Deita's route but instead watermage drops more and more hints about being in love with the MC. at the end of the war, during the last conversation with the gods, choose all the same options to "stay as the transient one" as shown above and there will be a scene where watermage leaves to get some tea for the MC and Jeth grabs the MC from the shadows, presumably kidnapping them.
Hope this helps!
Thanks so much for your feedback <3