Titled after her age when she started writing songs, the album consists of 15 tracks, including her breakthrough number-one single "Bansanka".

The song became her breakthrough, rising up to number one on both the Oricon Combined Singles Chart and Billboard Japan Hot 100 in January 2024,[1][2] and making her the youngest solo artist that have the song surpassing 100 million in Billboard Japan history.

[6] The limited edition of the album includes Usagi-san doll and "Special Book", including self-written liner notes, a conversation with Usagi, who runs Lunar Landing Plan label with the singer, and Q&A sessions.

[8] A music video for the third track "Pure Love Ingot" was uploaded on the same day as 15 release.

[9] "Moon Landing Plan", a namesake of Tuki's label, was chosen by Suzuki for Solio Bandit commercial's jingle, starring Kanna Hashimoto.