i was wondering does meroiko know mitsuki grandmother while she a shinigami if so what chapter does she know or when she remember
Chapters 17, 18, and 19 cover their meeting in the present and their history in the past.
Her Grandmother finds Meriko moving around in her plushy form and thinks that she is a troll. Being around Mitsuki's grandmother caused her to remember her past when they were best friends and that she killed herself because she thought that Mitsuki's grandmother had betrayed her with the person she loved. That was what had turned Mitsuki's grandmother against music. In the end things are straightened out and Meriko appears before her grandmother in her real human form, Meriko's Shinigami form is different from what she looked like when she was alive, and that allows Mitsuki's grandmother to say her apologies.