A dynacubus is naturally a spirit form which can take physical form either as male or female, like incubi and succubi. Unlike incubi and succubi, however, mating with a dynacubus results in the physical death of the human, by means of a violent explosion a split-second after sexual orgasm. This explosion releases the flesh of the human to be subsumed into the dynacubus, and the soul or spirit-force of the human to join into the gestalt that is an individual dynacubus. Once taken into a dynacubus gestalt, the individual spirit-forces are all bisexual, even if they had not been before.
The dynacubus seeks humans who are both sexually inclined as well as desiring of physical death. It does not select humans who are not currently in a state of thanaterotic desire. If a dynacubus senses a human who has a general thanaterotic desire but not a current desire for death, it will leave but will check back with that human years hence.
Once the dynacubus has found a thanaterotic mate, it forms into the appropriate gender for the human's desire. The dynacubus can make parts of itself form into explosives, or even parts of the human into explosives while those parts can still perform sexually if that is their normal function. For instance, a male whose thanaterotic desire involves his cock exploding to trigger his physical annihilation will have his cock transformed on the outside into a stick of dynamite, and he will feel the hardness of that dynamite as if it were the hardness of his cock - while still being able to produce an initial forceful spurt before detonating. The overall explosion is contained within the wings of the dynacubus, which fold tightly around the human just at the start of orgasm.
Upon each thanaterotic mating, the dynacubus gestalt shares the human's feeling of orgasmic explosion, and larger gestalts are capable of producing larger explosions. However, as the gestalt enlarges, the feeling is thinned out due to the number of beings within the gestalt. Eventually, one of the beings within the gestalt will become individually powerful enough to split off into another dynacubus. The split takes place immediately after a human mating; the initiator of the new gestalt, along with the most-recently taken human and the life-force of the currently-exploding human form the new, smaller gestalt.
If humans who have ties to other realms are taken from the physical realm by a dynacubus, they may eventually leave the dynacubus gestalt on their own and enter any other realm to which they have right. However, if they then leave that realm to re-enter the physical realm, they will always leave the physical realm by means of thanaterotic mating with a dynacubus unless they directly enter another realm as a means of exiting the physical realm.