Reindeer

Confined to the northern reaches of Older Sister and some of the Ares islands, reindeer have long held a position of cultural significance for the peoples in the north, particularly those who still live semi-nomadic lives. In addition to their domestication for use as mounts, reindeer provide rich dairy products and occasional meat, reindeer are used for religious ceremonies. Seers and priests in the north follow reindeer as the latter hunt for fly agaric mushrooms, and collect the urine of the reindeer after they eat these hallucinogens (as the mushrooms can be toxic to humans, but don't disrupt the health of a reindeer), and the urine is consumed to produce an ecstatic state.
Additionally, the reindeer' ability to see in the ultraviolet spectrum has lead to more secretive tribes marking paths or areas of interest with special paints unseen by the human eye, and allowing reindeer to lead the tribes that follow them, instead of the other way around. Newer generations are often not taught these routes, ensuring that anyone who tried capturing a tribal member or using marriage as a means of pressing a nomad to give up tribal secrets would find none.
The last area of significance for these noble animals lies in prophecy. Reindeer with red noses being born is considered an auspicious omen, and certain of these reindeer are set aside and given special treatment in anticipation of a sacrifice on the winter solstice. Reindeer horns are commonly associated with the Hunter, the goddess said to go forth during the winter solstice to chase the souls of the dead back to where they belong and bring in those who refuse to return. Fly agaric mushrooms are said to have links to the world of the dead, hence the ability of reindeer to hunt them so easily and the connection with the Hunter. Burial ceremonies in the north almost always include the skull of a reindeer in the grave to help the deceased find their way, and altars commemorating the dead in northern lands invariably contain reindeer bones.