Written by Ayase, the song was based on the light novel Monogatari writer Nisio Isin's short stories Nadeko Past and Shinobu Future.

"[6] He also revealed in a Comic Natalie interview that he wrote the song about the Monogatari character Hitagi Senjōgahara when he was 18–19 and often performed it live with his rock band.

[9][10] Five days later, they revealed the song's release date, to be July 1, 2024, and its cover artwork, featuring the character Yotsugi Ononoki making a V sign with both hands.

[11] "Undead" was sourced from two short stories written by Nisio, Nadeko Past (なでこパスト) and Shinobu Future (しのぶフューチャー), published on the anime's website on July 1, 2024, the same day as the song release.

[12] Both stories told the Monogatari characters Nadeko Sengoku and Shinobu Oshino lying on a sofa and receiving counseling from Yotsugi Ononoki about their nervousness.

[7] Tomoyuki Mori from Real Sound described it as a "perfect blend of kick and bass that reaches deep into the body," the track that "intertwines brilliant and sharp synth phrases," and the inorganic melody that reminisces about early Vocaloid music.