I thought she will wait at the entrance ? I manage to convinve her to betray the snake people , she ran away but we meet again in the portal…
Then i romance with her before the final battle , her scene was cute because she will follow me from behind for the final battle
The walkthrough is at the top post, perhaps you can scroll up have a look ? 
By @sljzz
How to romance Kiemia
Her romance starts really really late, in the middle of the final battle. In the mean time, do not romance anyone else (duh).
[spoiler]First, recruit her.
Step 1, convince her.This can be done in two ways:
When getting the tabulation chart, tell her “you don’t have to serve the False icon”. If you have high charisma and relationship >60 with her and aren’t serving the false icon yourself, she will turn against the snake people.
In the three way standoff with Stralchus and Keimia, say “I know you don’t want any of this”, and tell her to step aside (requires 60 valor or 65 charisma, plus Keimia relationship > 60).
If you’ve done either of these, then in chapter 12, after Control says, “We should attempt at least one strike at one of our enemies while we still have the time.”, there should be the option to contact Keimia and recruit her.
In chapter 12, in the middle of fighting the ziggurat/false icon, where the other ROs have their scene:
I seek out Kiemia
Tell her how I feel (requires showing interest previously)
Pull myself up the tree
You can escape this world (requires planning to go home)[/spoiler]
If someone makes this work, let us know 