Otherkin/therianthropy means you have a soul that isn't human, it is a mix of spiritual, maybe mental.
Being otherkin or therianthropy does not have any kind of need.

Vampyres on the other can have human souls, but the very definition of a vampyres is a being who NEEDS to take some kind of energy to function, remain healthy and worst case stay alive.

Psychic vampyres: A psychic vampyre is a general energy feeder that does require a physical conduits. People believe that psychic vampyres feed through a psychic connection of some sort.

Astral Vampyres: An astral vampyre is a spiritual or spectral vampyre that does not require a physical conduit. These vampyres tend to leave their bodies in some kind of energy form to feed.

Emotional vampyres: A emotional vampyre is a advanced kind of psychic vampyre. They feed off of extreme emotions, generally but not limited to anger. They have the ability to drain someone harder then a normal psychic vampyre.

Sanguine vampyres: A sanguine vampyre is a general physical energy feeder. They require a physical conduit which for a sanguine is blood.

Tantric Vampyres: Tantric vampyres are very similar to sanguine vampyres. The difference is that Tantric vampyres feed off of intimate activities. If their energy needs are high enough and do not know how to control their feeding it can endanger their partners lives. Another name for this is incubus or sucubus.
(i will add this to the vampyre section asap)

_______
Vampyres existences are believed to be caused by multiple different reasons, here are some examples: a damaged chakra, a chemical imbalance in the brain, some believe it could be caused by a physical energy deficiency.