In those days Caesar Augustus issued a decree that a census should be taken of the entire Roman world. And everyone went to his own town to register.
So Joseph went up from the town of Nazareth in Galilee to Judea, to Bethlehem the town of David, because he belonged to the house and line of David. He went there to register with Mary, who was pledged to be married to him and was expecting a child. While they were there, the time came for the baby to be born, and she gave birth to her firstborn, a son. She wrapped him in cloths and placed him in a manger, because there was no room for them in the inn.
Genryūsai Shigekuni Yamamoto stood solemnly by his captain. He was the Lieutenant of Squad 1, subordinate only to the Captain Commander and the Gotei 13. He had founded the Shinigami Academy only a few decades ago, and the whole concept of an organized class of shinigami was new in Soul Society. Out of respect, he had let his brother, Ousu Takeru Yamamoto, become the Captain Commander.
For millennia, shinigami had been the fighting force of Soul Society. Soul Society itself first came into being when the universe was created, splitting into the Human World and the Spirit Worlds. All of the Gods and Goddesses had fought each other for centuries, attempting to gain control of both worlds. The shinigami were their armies, fighting over land and power. Tsunamis, earthquakes, floods, drought, and all kind of calamities plagued the Earth. Each God appealed to a human civilization to attempt to gain power, but some Gods ended up perishing not because of other Gods, but because of the humans themselves.
Currently, Jupiter of the Romans dominated the Soul Society. However, the God of the Jews, Yahweh, was currently fighting in an open war against him. The shinigami, having been organized into a caste of warriors, were to be loyal only to the Gotei 13 of Soul Society, or the Shinigami King. Currently, Yahweh was the Shinigami King, while Jupiter was the head of the Gotei 13. This forced shinigami to constantly change loyalties and fight against each other.
However, Yahweh apparently had a different plan. He, like other Gods, would use the humans to his advantage. While he only had a small flock in Judea and Ethiopia, he had bigger plans. The Roman Empire was the source of Jupiter's power. Jupiter himself stole the throne from Zeus of the Greeks due to Greece being conquered by Romans. If Yahweh could collapse the Romans, or at least their faith in their Gods, he could be victorious.
So, according to his command, Ousu sent a shinigami with a message to a Jewish priest, to moreover warn them a savior was coming. In reality, a shinigami would use reincarnation to be born into the human world and attempt to sway the Judeans and Romans in order to weaken Jupiter and his pantheon. Yahweh would give the shinigami some of his power, and in return, the shinigami would be the right-hand man of Yahweh.
This is what Genryūsai and Ousu were there for. The shinigami was about to go to the human world and inhabit the body of a child. The child was special, because he was of the lineage of the greatest King of Judea, David. This would surely help him on his mission. Yahweh, clad in white robes and smiling, walked with the man to the gate to the human world. Genryūsai couldn't help but wonder how all of this would turn out. If the 'savior' failed, they would be killed for being on the wrong side. He hoped that the boy wouldn't disappoint them…