Okina Matara is a hidden God of multiple faces and roles. Eternity Larva is a lowly fairy that Okina hints to actually be a god.
From the touhou wiki.
"When Okina Matara wonders if Eternity is actually the Tokoyo god, she states that the Tokoyo god is one of her enemies.
This may allude to the fact that the cult of the Tokoyo god was brought to an end when the leader of the cult was arrested and executed by an official named Hata no Kawakatsu. Later, Hata no Kawakatsu would occasionally be equated with Matara-jin due to their similar divine natures as gods of the performing arts"