Sankarea: Undying Love

Chihiro Furuya has been fascinated with zombies since childhood, and when his cat Baabu dies, he decides to create a resurrection potion to bring him back. This endeavor leads him to meet Rea Sanka, a wealthy girl who's been struggling with her life and has a peculiar habit of ranting into an old well. Chihiro eventually succeeds in reviving Baabu, but Rea takes the potion by mistake, thinking it will end her life. Instead, she dies and is reborn as a zombie, forcing Chihiro to navigate the consequences of her new undead state.