Ippongyō waka kaishi (Poems on the Chapters of the Lotus Sutra)

Aristocrats of the Heian period were in the habit of carrying around slips of paper called kaishi in the bosoms of their robes for use in impromptu poetry composition. This work is a collection of poems on kaishi written by some of the most famous poets of the late Heian period, including the poet-priests Saig yō (also known as En’i, 1118–1190) and Jakuren (1139–1202). Each poet wrote two poems on the theme of one of the twenty-eight chapters of the Lotus Sutra. From the official titles with which the poets signed their names, we can date the production of this work between the years 1180 ( Jishō 4) and 1182 ( Juei 1), though some scholars have suggested that the poem by Saigyō could not have been written during the same period.
The set is thought to have originally comprised a total of either twenty-eight or thirty sheets (with the addition of poems on the prologue and epilogue sutras comprising the Threefold Lotus Sutra); only fourteen sheets survive today.With the exception of the Saigyō poem, which is mounted as a hanging scroll, each of the poems is mounted as a folio, resembling one leaf of an album. Remarkably, an essay entitled Baisō hikki (Notes of the Plum Window) by Hashimoto Tsuneakira (1755–1805) mentions that at that time the Nara Temple of Ichijō-in (part of the Kōfuku-ji temple complex) was in possession of fourteen poems written on kaishi, which had been composed on sutra-related themes by such poets as Saigyō and Jakuren. Thanks to this mention, we know that only these same fourteen poems of the set survived until the Edo period. The poem sheets each have a fold in the middle, and there are traces of what appears to be copies of Buddhist texts on the back, suggesting that the backsides of the sheets were used as a booklet in the distant past.
These fourteen are the oldest surviving poems on kaishi sheets in Japan. They are considered all the more significant due to the poetic luminaries who composed and transcribed the poems. In addition, while numerous fragments of calligraphy are attributed to the priest Saigyō, only a handful of these are considered unmistakably authentic—further increasing the importance of this particular work.