Kourin begins as Kou Shuurei's lady-in-waiting and later marries Tou Eigetsu. Adopted by Sa Enjun and Hyou Eiki, she exhibits profound loyalty to Enjun and the Sa clan. When Emperor Ryuuki rejects Enjun's granddaughter as a consort, seemingly favoring Shuurei, Kourin poisons both Shuurei and herself to avenge the perceived insult to the Sa clan and protect Enjun.

After Enjun's death, Kourin moves to Sa province to live with Hyou Eiki. She later travels back to the capital with Ro Ensei to deliver news of an emerging crisis. During the return journey to Sa province alongside Ensei, Shi Seiran, Tou Eigetsu, and Shuurei, captors mistake Kourin for Shuurei and kidnap her. Imprisoned with Eigetsu, she convinces her captors Meisho and Sa Soujun of her false identity by successfully rewriting the famous poem of poet Mei Senshi. They escape to Kinka with Sa Kokujun's aid.

Reunited with the group in Kinka, Kourin exhibits complex emotions toward Eigetsu, marked by concern, annoyance, and exasperation. As Eigetsu's bond with the immortal Yōgetsu weakens, he confesses his love to Kourin and kisses her before departing. They reunite after Yōgetsu enters hibernation, freeing Eigetsu to stay with her. Kourin then chooses to remain in Sa province serving Eigetsu.

Her skills include proficiency in domestic tasks like cooking and cleaning, honed during her service as Hyou Eiki's maid. She also possesses notable knowledge and intelligence, demonstrated during Soujun's identity test. Kourin is 13 years old during her service as a lady-in-waiting.