Ningyo no Kubi

Maki, a shy girl, has lost her beloved senior to her friend Rumi. Jealous of the proactive Rumi, Maki has an eerie dream in which a woman's severed head speaks. "I'm a mermaid... eat me... and you'll surely become beautiful." Maki, who has listened to the mermaid's whisper, is faced with a shocking future...!? In addition to the title story, this masterpiece collection of short stories includes the mermaid series "Siren" and "The Sea Where Mermaids Live," "The Flower's Name," which depicts liberation from the curse of the past, and "The Dream Continues," which depicts the tragedy brought about by love and hate!

(source: Amazon.jp, translated)