Furude Ōka (古手 桜花, Furude Ōka) is the daughter of Hanyū and Furude Riku. Though reluctant, she is the one who performed the Watanagashi ceremony on Hanyū, because Hanyū felt that Hinamizawa would become calm if she died. She created the chip on Hanyū's horn. Ōka most likely started the myth of Oyashiro-sama's curse.
Rika is the direct female descendent of Ōka, which explains why she can always see Hanyū.
The two also look very similar with the only difference being their slightly different hair color.