Shinigami

In Gensokyo, A Shinigami is someone who brings souls to the Yama (or Enma) Shikieiki Yamaxanadu. Gensokyo's only known shinigami, Komachi Onozuka, ferries souls to the Higan. This is apparently done by crossing the Sanzu River.

While Komachi is a ferryman of the Sanzu, not all shinigami occupy this position. For good reason, most people assume their life is over at the sight of a shinigami, but only a few are actually charged with taking the souls of the expired. These shinigami may be fought with just as any other creature, allowing stronger youkai to continually prolong their lifespan. Celestials are notorious for this, disguising their victory as guaranteed immortality.

According to some people they have long lifespans which means they aren't immortal, as they can be killed by either getting sick or being cut up. There is also another theory saying that it can die if it saves a person from how it is supposed to die.