Eua

Eua is a powerful, supernatural being either living in or visiting the kakera world. Her powers are similar to but far stronger than Hanyū's. Just like Hanyū, she can rewind time and grant people the ability to "loop" via the endless number of kakera, but unlike her, Eua can also grant people the ability to retain their complete memories of previous loops. However, she says this ability can only be activated through the person dying, which implies that she not an omnipotent being, unless she was lying and just enjoys attaching that condition.

(Source: Higurashi no Naku Koro ni Wiki)