Not to be confused with Succubi_(Echidna)
Succubi, and their male counterpart, Incubi, are a yokai race native to Terra'su's Moon, Jigoku, created as a side effect of Izanagi's cleansing of his body and spirit of Tomi's, the underworld's, influence, and unexpectedly, his own lust. Due to the association with the cleansing rite, Succubi are often regarded as demons.
After Izanagi's lust had taken a physical form, it fled to the moon, Jigoku, and slowly grew into sentient creatures that would eventually become the succubus species and establish connections between Terra'su's Kitsune, and the "Shin Tsukians" from Tsuki. While Tsuki mostly remained its own independent world, the succubi and human leaders of Jigoku united Terra'su and Jigoku's governments.
In terms of appearance, succubi and incubi have a wide variance of looks to them, but common features can be bat like wings on the back of head, horns, and spaded tails. Outside of their true forms, the cubi have a massive ability to shapeshift between forms they may desire. It's not uncommon for a succubus's pupils to take on the appearance of hearts when in the right mind set.
Due to being originally derived from Izanagi's lust, Succubi and Incubi can feed on sexual and lust energies kicked up from the heavy emotion during intercourse, and this is, in fact,the primary method of feeding for cubi. Secondary, and far less popular, methods include draining someone's life force out during intercourse. Once sexual energy is converted in a way that can nourish a being, a portion of it can even be sent to a cubus's partner.
While a deceased soul, if consumed by enough lust, can become a succubus, this isn't necessarily the primary means of reproduction. That being said, succubi only become pregnant if they choose to have a child.
Both Succubi and Incubi can breed with any other humanoid species, due to being a being primarily composed of magic and lust energy. The lust energy and magic will fuse into the child during the pregnancy resulting in a hybrid.