《Sea Red》 - Kaikou

...This was the beginning of the free-style haiku movement, and in 1914 (Taisho 3), Ogiwara Seisen-sui joined the movement, advocating even bolder free expression and the unnecessary use of seasonal themes in the haiku magazine Soun, and in 1917, Kawato Hekigoto also joined the movement, arguing that colloquial expression was unavoidable. From the perspective of haiku magazines, the free-style haiku movement was centered on Kaikou (the successor to the aforementioned Daisaku), and Soun, with Hekigoto's Heki and Samadhi, and Kuribayashi Issekiji and others' Haiku Life. However, after the deaths of Hekigoto and Ippekiro, Soun became the mainstream, and it was joined by a part of the New Haiku People's Association's journal Haiku People, Yoshioka Zenjido's Milky Way, and others, which promoted free-style haiku after World War II.

*Some of the terminology explanations that refer to "Sea Red" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…これが自由律俳句運動のおこりで，1914年(大正3)には荻原井泉水が俳誌《層雲》でいっそう大胆な自由表現と季題無用論を唱えて加わり，さらに17年には河東碧梧桐も口語表現のさけがたいことを論じて運動に投じた。これを俳誌の面からいえば，前記《第一作》の後身《海紅（かいこう）》と《層雲》を主流として，碧梧桐の《碧》《三昧》，栗林一石路らの《俳句生活》を加えたものが自由律俳句の流れであった。しかし碧梧桐，一碧楼の没後は《層雲》が主流となり，これに新俳句人連盟の機関誌《俳句人》の一部，吉岡禅寺洞の《天の川》などが加わり第2次世界大戦後の自由律俳句を推進した。…

※「《海紅》」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報