"" Means "once in a lifetime" in Japanese.
Jian Jia decided to enter Mu Liangcheng's world. She accepted Mu Liangcheng and his world. No matter how dark his world was, she believed that she could live like the sun lighting up his world, and that he and she could bathe in the sunshine.
Purpose: Love is a redemption, allowing people in darkness to bravely bathe in the sunshine.