Taneda Santōka regularly contributed to Ogiwara Seisensui’s haiku magazine Sōun.
Sōun, written 層雲 and often translated as “Layered Clouds,” was an important platform for Japan’s free-form haiku movement. Santōka became a disciple of Seisensui in 1913 and regularly submitted poems to the magazine. By 1916, he had also become an editor.
Seisensui promoted haiku that could move beyond the conventional 5-7-5 pattern and, increasingly, beyond the requirement for a seasonal word. Santōka’s later poetry became famous for its direct, wandering voice and its use of free rhythm, reflecting the movement’s emphasis on personal expression rather than strict formal rules.
The other options belong to different literary contexts. Myōjō was associated with romantic poetry, Araragi with tanka and related literary circles, and Hototogisu was a major haiku magazine linked to the more traditional line of Takahama Kyoshi. Sōun is specifically the publication tied to Santōka’s relationship with Seisensui and free-form haiku.