The Legendary Spirall Shell appeared in Mermaid Melody Pure episode 12. It lied in the Indian Ocean Graveyard and belonged to Sara and contained all of her past emotions which Sara sealed away in this shell. At first, the Black Beauty Sisters found it and broke the seal on the shell, released the negative feelings from it, and tried to use it aganist the Mermaid Princesses. However, the love Sara had for Tarou was ultimately released from it and Coco, Lucia, Hanon and Rina were able to defeat Sheshe and Mimi. Sara's Shell is now in peace.
The legendary spirall shell can keep a seal on the unwanted memories and emotions of the user, and, by releasing negative feelings from itself, upgrade evil songs like Yami no Baroque.
After the shell had been put at peace, Seira's image appeared telling Lucia and the others that she had been the one who had encouraged Coco to go search for it.