Iwasaku and Nesaku (イワサク・ネサク)

Iwasaku (also called Ihasaku) and Nesaku were gods (Shinto religion) appeared in Japanese Mythology. Their names were written as 石析神 and 根析神 in Kojiki (The Records of Ancient Matters) and 磐裂神 and 根裂神 in Nihonshoki (Chronicles of Japan).

In the chapter of kamiumi (bearing gods between Izanagi and Izanami) in Kojiki, when Izanagi cut off the head of Kagutsuchi, the god of fire, who was the cause of his wife Izanami's death with his Totsuka no tsurugi sword, they metamorphosed into gods when the blood on the sword stuck to the rock, and Iwatsutsunoo metamorphosed next. It was same for the sixth alternate writing in the same chapter in Nihonshoki. In the seventh alternate writing, it said that Iwatsutsu no onokami and Iwatsutsu no menokami were born as the children of Iwasaku and Nesaku, and the child of those gods was Futsunushi no kami.

In Kojikiden (Commentaries on the Kojiki), it said that their name should have written as '石根析' (Iwanesaku) but it was divided into two and named their Shinmyo. Saku' was from Norito (Shinto prayer) of 'Iwane Kine Fumisakumite,' and it indicated that there was a rough patch on the rock.
TACHIBANA no Moribe picked out 'Saku' as '裂く' (pronounced as saku, meaning tear) and interpreted that it described 'the power of sword to tear even the root of the rock.'