Triwia, the princess of the Moon Kingdom, was under house arrest in a castle.
One day, taking advantage of the festivities, she escapes from the castle and meets a boy with mysterious eyes.
"When you grow up, let's travel around the world together."
Finding a kindred spirit in him, she accepts his promise, and with that promise in her heart, she returned to her normal, constrained life.

Eight years later, she has grown into a splendid adult
After her coming of age ceremony, which was scheduled for the following day, she planned to set out on her journey.
To fulfill a promise she made to a man she met long ago.
However, a tragedy strikes her.
This is a strange story of a princess that begins with a promise.