Halzion

"Halzion"
Single by Yoasobi
from the EP The Book
LanguageJapanese
ReleasedMay 11, 2020
GenreJ-pop
Length3:18
LabelSony Japan
Songwriter(s)Ayase
Producer(s)Ayase
Yoasobi singles chronology
"Ano Yume o Nazotte"
(2020)
"Halzion"
(2020)
"Tabun"
(2020)
Music video
"Halzion" on YouTube
English version on YouTube

"Halzion" or "Harujion" (ハルジオン; lit. "Philadelphia fleabane") is a song by Japanese duo Yoasobi from their debut EP, The Book (2021). It was released as a single on May 11, 2020, through Sony Music Entertainment Japan. The song depicts the protagonist who spends days of disappointment after parting with her lover, finding hope while re-questioning her dreams and the meaning of life, and regains her motivation to move into the future. The English version of the song was included on the duo's second English-language EP E-Side 2, released on November 18, 2022.

"Halzion" was based on Soredemo, Happy End, a short story written by Hashizume Shunki, marking the first time that Yoasobi collaborated with a professional novelist. Unlike the duo's former two songs, the source material was not based on the novel-centered social media Monogatary.com. The song and the story it is based on were released as part of an advertising campaign Immersive Song Project by Suntory, to promote their new energy drink branded Zone.