Seireki13ya

 (星歴13夜) is an idol group under codomomental formed on December 15, 2018, and debuted on December 25, with a digital single.

Their concept is "今夜のかなた 夜のくに" (Unofficial translation: Night-land, faraway tonight). A unique fictitious constellation is assigned to each member.

On August 12, 2021, it was announced that the group would enter a hiatus following the termination of contract of Shiki Towa.

On December 8, it was announced the withdrawal of Ama Mauru and an audition for new members.

On November 26, 2022, they announced a new line-up.

Current Members

 * Nene Komochi (寝こもち; ) (Original Member)
 * Yui Urari (結うらり) (Joined November 26, 2022)
 * Who Runo (誰るの) (Joined November 26, 2022)
 * Yoha Minai (世みない) (Joined November 26, 2022)

Former Members

 * Fuwa Akane (浮あかね; ) (Original Member; Graduated March 26, 2021)
 * Sono Homare (園ほまれ; ) (Original Member; Withdrew July 24, 2021)
 * Shiki Towa (色とわ; ) (Original Member; Contract terminated August 12, 2021)
 * Ama Mauru (天まうる; ) (Original Member; Withdrew December 8, 2021)

Timeline
Note: - Member on Hiatus

Concept
's overall style is "dreamy/night" as their name roughly translates to "Astral Calendar of the 13 nights". Their music style is upbeat EDM/Eurobeat.

Their introduction on their site read: English= "Beyond Tonight, Land of Night"

The land of the night that connects this world and that world. Over the thirteen nights are the five star groups of the constellation Amaoto, the Whisperer on a lonely night, the constellation Icosaurus, the constellation Hot Miruku, and the constellation Bedwetting. Even if you count the years, you will probably lose track of which world line you are in. Good night future. 「今夜のかなた 夜のくに」
 * -|Japanese=

こちら世界とあの世界、ちきゅうぼし繋ぐ夜のくに. 13の夜を超えるのは、あまおと座・さみしい夜にささやき座・未明わるいこ座・ほっとみるく座・おねしょ座の5星群. 指折り暦を数えても、きっとどこかわからなくなっちゃう世界線. おやすみ未来.

History
2018=
 * On October 1, there was an announcement of audition to recruit members.
 * On December 6, the group's visual and the members were shown.
 * On December 15, they debuted at the "コドモメンタル女子遊戯～たなとす vol,3～" live.
 * On December 25, they uploaded a pre-debut digital single titled Sekaisengoto.
 * -|2019=
 * On January 23, their first single Oyasumi Mirai to Koiotome was released.
 * On March 31, they held their first one-man live at Shibuya Chelsea Hotel titled "Seireki13ya First one-man LIVE ~13 nights~".
 * On April 21, their second single, Itoshi Utakata to was released.
 * On June 9, a free Mix CD STARRYPOP was given out.
 * On August 14, their third single, Yocto Asterism was released.
 * On October 13, they held a free one-man live at Tokyo's Shibuya eggman.
 * On November 27, their first album, Hugdreamy Horoscope was released.
 * -|2020=
 * On January 25, they held a one-man show at Shinagawa Intercity Hall, Tokyo, titled "Solo Performance ~Starmare Memory~".
 * On January 28, it was announced the group would have their first nationwide tour titled "FemtoNovaSet Tour". It was sadly heavily affected by the COVID-19 pandemic, but managed to start up afterwards. To make up for the canceled shows, the group did YouTube Lives to chat with the fans.
 * On March 18, their fourth single, Ai ka Higurashi was released.
 * On June 17, their fifth single, Baby baby Cupid was released.
 * -|2021=
 * On February 10, their first mini album, Akashic Records was released, which contains solo songs by the members.
 * On February 17, "Teenage Melancholy", a photobook of Shiki Towa and Ama Mauru, was released.
 * On March 20, Sono Homare went on hiatus.
 * On March 22, Fuwa Akane withdrew from the group.
 * On April 4, auditions for new members were held.
 * On May 12, their second album, MythEpoc, was released.
 * On July 24, Sono Homare withdrew from the group.
 * On August 12, Shiki Towa's contract was terminated, and the group went into a hiatus.
 * On December 8, Ama Mauru withdrew from the group.
 * An audition was announced.

Albums

 * 1) [2019.11.27] Hugdreamy Horoscope
 * 2) [2021.05.12] MythEpoc

Mini Albums

 * 1) [2021.02.10] Akashic Records (アカシックレコード)

Singles

 * 1) [2019.01.23] Oyasumi Mirai to Koiotome (おやすみ未来と恋乙女)
 * 2) [2019.04.10] Itoshi Utakata to (愛し泡沫ト)
 * 3) [2019.09.15] Yocto Asterism (ヨクトアステリズム)
 * 4) [2020.03.18] Ai ka Higurashi (哀唄日夜)
 * 5) [2020.06.17] Baby baby Cupid
 * 6) [2020.10.21] Romantic Escape

Digital Singles

 * 1) [2018.12.25] Sekaisengoto (せかいせんごと)

Mix CD

 * 1) [2019.06.04] STARRYPOP