This temple was formerly the residence of Yadoya Mitsunori, a vassal of the Regent Hojo Tokiyori. Nichren wrote the Rissho Ankoku Ron or " Establish the Right Teaching and Save Our Country", an advice to the government, and submitted it to the Regent thourgh the hand of Tadoya Mitsunori in 1260. When Nichiren was persecuted in 1271, his disciple Nichiro was put in a dungen halfway halfway up this hill Mitsunori converted himself to the religion of Nichiren, and remodelled his residence to this temple called after another pronounciation of his name.

The flowers of Kosokuji Temple:
January: Suiren (Nymphaea), Tsubaki (Camellia japonica), Robai (Chimonanthus praecox)
February: Ume
March: Hakumokuren (Yulan magnolia), Peach
April: Sakura, Hangesho (Saururus chinensis)
May: Tsutsuji (Azaleas), Fuji (Wisteria), Botan (Peony)
June: Ajisai (Hydrangea), Hanashobu (Japanese iris), Ayame Iris
July: Lotus, Kikyo (Platycodon grandiflorum)
August: Sarusuberi (Lagerstroemia), Suifuyo (Hibiscus mutabilis)
September: Hagi (Lespedeza), Higanbana (Amaryllidaceae)
October: Rindo (Gentiana)
November: Sazanka (Camellia sasanqua)
December: Autumn fall.