Incorporeal Movement. The Seishin's projection can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.

Summoned Spirit. The Seishin is bound to the soul of another creature. As an action on their turn, the host creature can summon the Seishin projection or, as a free action, temporarily dismiss it. When summoned, the Seishin projection appears in an unoccupied spot within 5 feet of the host creature. The Seishin projection is dismissed if it falls below 0 hit points. If the Seishin projection is dismissed in this way, it cannot be summoned again until the host creature has completed a long rest. The Seishin projection cannot travel more than 120 feet away from the host creature. If the host creature moves out of the range of the Seishin projection, the Seishin projection is dismissed and the host takes 7 (2d6) Psychic damage.

Uniting Bond. The bond between the Seishin projection and the host creature cannot be broken except by a Wish spell.

Like-Minded. While bound to a host's soul, the Seishin can communicate telepathically over any distance and through any object with its host, regardless of if the Seishins projection is summoned or dismissed.

Familiar Independence.  The Seishin projection acts independently of the host creature but always obeys the host's commands unless those commands endanger itself or the host. In combat, it rolls its own initiative and acts on its own turn. It can't attack, but it can take other actions as normal. When not given a command, the Seishin projection prioritizes protecting itself and the host creature.

Perception is Reality. The Seishin projection can manifest as either an opaque, realistic representation of their animal form or as an ethereal, slightly transparent representation of their animal form. The complexity or lack-there-of of any trinkets, runes, or other symbology on the Seishin projection is determined by the host upon summoning. While in its ethereal form, the Seishin projection emits a dim light with a radius of 5 feet.

Scaling. If the host is a player character, the max HP of the Seishin projection is 9 + 3 * the player character's total level.

Afterlife.  The Seishin projection doesn't require air, food, drink, or sleep.