Plum

Plum/Zeta is Kairo's pet octopus, which he cherishes and loves very deeply. Throughout the story, he often is seen walking around the house.

Death
In S2EP5, Plum is actually named Zeta, but due to very weak health she died when Kairo was young and she was erased from his memories.

As Zeta
Throughout the series, she only appears in Sun-Hi's dreams. Eventually, Zeta reveals that she created Plum: the pet who died 4 years ago and the pet who grew up with Kairo was a clone she made so that he would not forget her. Zeta is actually the real Plum!

Relationships

 * Zeta - Plum is Zeta's clone. She is the real Plum.
 * Kairo Tanaka - Kairo's pet octopus, which he cherishes and loves very deeply as a child.
 * Sun-Hi - She frequently appears in Sun-Hi's dreams as her Guardian. As 'Plum', they have some kind of tsundere relationship.