Nico

Nico is a Silver Key Celestial Spirit owned by Katja.

Appearance
Nico is a short, stout green creature with pale green marks on the back of its head. Nico also has a pair of bland eyes and a golden horn-like nose. Its body often shakes nervously, though this doesn't always occur.

Key of the Starry Sky arc
Note: Events in this arc occur only in the anime and do not constitute canon material. Nico is summoned by Katja to watch the tree with her while being carried.

As its owner, Katja asks it how long the tree will live. Somebody tells Katja not to wander off, and she tells the spirit if it is scared it can escape. When Katja and Nico are inside a cathedral, Doranbolt and Lahar come to visit her and Nico. Racer appears and his target is Katja.

As Katja's Magical Power starts to fade due to the Anti Link, Nico also begins fading away. Katja thanks it before it completely disappears.

Magic and Abilities
Immortality: As a Celestial Spirit, Nico cannot die, unless it is forced to stay in the Human World somehow.