Perfected creature existence can be attained, sustained, and eternalized by the fusion of self-conscious mind with a fragment of the pre-Trinity spirit endowment of some one of the persons of the Paradise Trinity, either Father, Son, or Spirit. 
In the fusion experience there is no overlapping; the will creature is either Spirit fused, Son fused, or Father fused. Those who are Adjuster or Father fused are never Spirit or Son fused. 
When a human being has completed the circles of cosmic achievement, and further, he has realized the final choosing of the mortal will then the fusion of the Adjuster and the morontial soul happens.
Almost 90% of the inhabited worlds of Nebadon are peopled with Adjuster-fusion mortals in contrast with a near-by universe where scarcely 50% of the worlds harbor beings who are Adjuster-indwelt candidates for eternal fusion. 
Fusion with the Adjuster is usually effected while the ascender is resident within his local system. It may occur on the planet of nativity as a transcendence of natural death; it may take place on any one of the mansion worlds or on the headquarters of the system; it may even be delayed until the time of the constellation sojourn; or, in special instances, it may not be consummated until the ascender is on the local universe capital. 
Some mortals fail to fuse with Adjuster without error due to the mortal. Then the Adjuster leaves, and upon this leave-taking the morontia mortal is immediately fused with an individualized gift of the spirit of the Creator Son.  The spirits of mortal fusion always ascend to the level of origin; such spirit entities unfailingly return to the sphere of primal source. 
The fusion ceremony is very simple. The morontia associates of the survivor say, “This is a beloved son in whom I am well pleased,” and this marks the entry of the ascending mortal into the eternal career. 
Such fused beings are twofold in their universe reactions: They are discrete morontia individuals not altogether unlike seraphim, and they are also beings in potential on the order of the Paradise finaliters. 
With Adjuster fusion begins the human attempt to realize and to actualize the limitless possibilities that are inherent in the supernal partnership with God which has thus factualized. 
After the fusion of the immortal morontia soul and the associated Adjuster, all of the experience and all of the values of the one eventually become the possession of the other, so that the two are actually one entity. The mortal gains Adjuster’s memory of all previous mortal indwellings.  When fusion with the Adjuster has been effected, there can be no future danger to the eternal career of such a personality.  Mortals are denominated ascending sons after fusion. 
Fusion is the act of breaking fetters of time.  Union with Adjusters is what confers oneness of soul with God and eternal life.  Fusion with the indwelling Thought Adjuster equals everlasting self-identification with total and indestructible reality. 
It is the personality synthesis of man and the essence of God; the factual experience of eternal union with God as a universe associate of Deity; inner union with indwelling God fragment.  It is the irrevocable choice for eternal career.  Fusion with the Thought Adjuster marks our mortal’s third jubilee. 
Celestial fusion is that never-ending blending of identity, that oneness of being which is so perfect and final that even the most experienced personalities can never segregate or recognize as separate identities the fusion partners. 
Fusion is the secret of the sacred sphere of Ascendington, and no creature, save those who have experienced fusion with the spirit of Deity, can comprehend its true meaning.  Fusion is the union of soul with Adjuster. 
Enoch was the first person on Urantia to achieve fusion during his earthly life.  Elijah the prophet fused during his life in the flesh.  Jesus attained perfect synchrony with Adjuster prior to baptism. 
Ordinarily, when a mortal of the realm attains such high levels of personality perfection, there occur those preliminary phenomena of spiritual elevation which terminate in eventual fusion of the matured soul of the mortal with its associated divine Adjuster. 
Glorified beings of final phases on an evolving planet are exempt from passing through the portals of death; they are submitted to Son seizure; they are translated from among the living and appear immediately in the presence of the Sovereign Son on the headquarters of the local universe. 
This experience of translation from the material life to the morontia state—fusion of the immortal soul with the indwelling Adjuster—increases in frequency commensurate with the evolutionary progress of the planet. During the era of light and life translation from living happens in morontia temple. 
On the merger with the Son, see link on mortals merged with the Son.
On Spirit Fusion, see link on Spirit-Fused Mortals.