Annanu and Enkidu were, in a sense, [one entity].
In the distant primordial age, Enki, the god of water, had descended deep into the underworld and retrieved the red clay from where Abzu's corpse lay—the red clay of the second-generation gods, still constantly merging. He used it together with his wife, Mami, the goddess of fertility, to create humanity.
Those were the first humans, free from the limits of lifespan and the burdens of exhaustion.
Yet Enlil, the great god, grew weary of such humans and ultimately attempted to destroy humanity four times in succession. In the end, however, at Enki's request as the father god, humanity was still granted a sliver of hope for survival.
Creating humans twice had nearly exhausted all the red clay Enki had brought back from the deepest reaches of the underworld, but he still had a little left. Just a little.
Later, Ishtar entered the underworld and was killed by her sister Ereshkigal. In order to rescue this goddess, who was crucial to humanity and the world, Enki used his remaining red clay and the water of life to create two genderless humans, Kurgarru and Galatur. He granted them the right to freely enter and leave the underworld, thereby freeing Ishtar from the predicament of death.
And in this incident, Enki finally gave away the last bit of red clay in his possession.
This final red clay was Annanu and Enkidu.
Utu borrowed the clay from Enki and created these two lives separately, bestowing upon them many powers before entrusting Enki with sending them into Enlil's forest.
But as mentioned before, Utu—
Was not exactly a quick-witted god.
The marriage he arranged for his younger sister could be called a failure of unprecedented proportions.
Ishtar's husband, Dumuzi, was still imprisoned in the underworld.
So