Aimer’s 23rd single titled Shiroiro Kagerou became available for digital streaming and download on October 4, serving as a prerelease before the full release on December 6. The title track joins as theme song for the second season of the NHK live action series Ooku, which premiered on the day before the prerelease.

Shiroiro Kagerou is a wistful and introspective ballad that is well-suited to Aimer’s husky and haunting vocals. Her emotional and introspective music has been featured in many favorite television dramas and anime shows, and it’s no surprise to see her music used for a series that explores complex themes of society and gender roles.

The live-action television drama Ooku is an adaptation of Fumi Yoshinaga’s award-winning manga, Ooku: The Inner Chambers. The story is a historical fantasy set in Japan’s Edo period, where a strange disease targets the male population and reduces it by seventy-five percent. Gender roles are reversed as women take on roles traditionally performed by men, including the shogun (military general). The story centers around the shogun’s “inner chamber”, where the most beautiful men are sent to serve.

Aimer commented on Twitter:

I created this song to accompany “Ooku” and the many people who lived in those turbulent times. I hope it will also resonate in your hearts as you live in turbulent times over 100 years later.

Physical copies of the single will become available for purchase on December 6.

Artwork for the prerelease of single “Shiroiro Kagerou”.