The blood, caught upon the swords hilt formed this kami. This is related in the kojiki and nihongi.12
However the nihongi also says they are the first of three siblings, not two born from this blood, the other two being Kuramitsuha and Kurayamatsumi.2
The Engi Rites says they have lots of Shrines throughout Japan. In a poem from the Man’yōshū (2:104) they summon snow down upon a hilltop where they are worshipped.1
1. Yasumaro. O, translated by Gustav Heldt. (2014) “Kojiki. An Account of Ancient Matters”. New York: Columbia University Press. 2. Aston. W.G. (1896) “Nihongi Volume 1: Chronicles of Japan from the Earliest Times to AD697”. Tuttle Publishing.