Spirit of Water

The Spirit of Water (水の精霊, Mizu no Seirei), is a spirit that has forged a contract with Montmorency de Montmorency and her family.

Background
The Spirit of Water is an immortal spirit that has existed presumably even during the time of Brimir as they have known and most likely interacted with Gandálfr. The latter once made a promise with the Spirit of Water, and they have since trusted Gandálfr.

In the past, the Montmorency family has bound a contract with the Spirit of Water until Montmorency de Montmorency made a contract with the Spirit when her father brought her to Lake Lagdorian.

At some point, the Spirit of Water has guarded the Ring of Andvari when it was stolen by Cromwell. As a result, they began locating the item, even to the point of flooding the area around Lake Lagdorian.

Appearance
The Spirit of Water is a formless glob of water that takes the form of a person, presumably someone it has bound a contract with; in the case of Montmorency, the Spirit vaguely looks physically like the latter, though it is unknown whether this is their true form or a coincidental matter. When taking the form of a person, they are gigantic in size, as seen when they had a conversation with Saito Hiraga, Guiche de Gramont, and Montmorency, and later together with Kirche von Zerbst and Tabitha. They also seem to be tip-toeing on the surface of the water, which also serves as a source for them to appear from.

Academy Summer Vacation
After Louise mistakenly drinks a love potion, Saito, Louise, Montmorency, and Guiche go to Lake Lagdorian to meet with the Spirit of Water to undo its effects. Along the way, the area near the lake is heavily flooded; Montmorency deduces that the Spirit of Water is upset. At sunset, Montmorency commands Robin to contact the Spirit of Water. Later, the Spirit emerges; Montmorency introduces herself and asks for a piece from the Spirit, but they decline. Saito begs the Spirit to offer them the Spirit Tear in exchange for anything they wish him to do. The Spirit asks them to fend off attackers, which Saito promises to defeat. Later, the group goes back to the Spirit of Water to ask the reason behind its anger. The Spirit tells them that their possession — the Ring of Andvari — was stolen by someone called Cromwell, leading them to overflow the water in search of it; Saito promises to find and return it. The Spirit believes him, recognising him as Gandálfr who once kept an oath to the Spirit in the past, hence offering them the Spirit Tear.

Trivia

 * The Spirit of Water speaks in the plural first person perspective when referring to themselves.

Quotes

 * "Someone abducted the treasure we were guarding. [...] We can exist only in water. Therefore, should we fill this entire world with water, we will someday have the treasure back in our hands."
 * (To Saito) "Gandálfr kept oath with us in the distant past. If it is Gandálfr, it is worth believing."