After the events of Requiem Zero, Lelouch dies and appears in Soul Society. He has no Geass, he is almost defenseless.
He decides to keep his first name, but decided to completely change his last name (or decided to be called L.L. in memory of С.С.). Events take place 150-250 years before the creation of the Vizards by Aizen.
Aizen is the reason why Lelouch ended up in the Soul Society. Aizen found a way to get into the world of Lelouch (natural seikaimon or Aizen's personal development, it doesn't matter) and decided to "put" Hollow in his head at the moment when C.C. gave him Geass, and because of this, it could seem that he is going crazy because of Geass.
Aizen is watching over Lelouch and Hollow within him which progressed throughout the Black Rebellion and Requiem Zero. One of the reasons for Requiem Zero was that Lelouch felt that he was losing control of his body and that the Hollow was taking control (even though he didn't know what exactly was happening to him at the time).
Deciding that the appearance of someone like Lelouch would cause chaos that could draw attention away from him in Soul Society, Aizen sends him there after the Requiem. Lelouch's death did not free him from Hollow, and over time, with great effort, he was able to come to some sort of an agreement with Hollow and, in fact, became the first Vizard and kept it a secret from everyone.
He goes through the Shinigami Academy, where he excels so much in learning Kidō that everyone expected him to join the Kidō Corps after graduation, but Lelouch decided to go to the second division (mainly due to the fact that he did not want to be weak as in life), where he develops his abilities and changes physically, becoming taller and eventually grows to the level of captain and appointed captain of the 10th Division, and become friends Ukitake and Kyoraku. Of all the people in Soul Society, only four (five) know about his past: Yamamoto, Ukitake, Kyoraku, and Unohana (and Aizen, of course).
Becoming captain, Lelouch spent almost 50 years looking for a way to return home at least for a while to find out what happened to his friends. Then the events of Bleach begin, in which Lelouch takes an indirect part. When Aizen leave Soul Society, Lelouch learns that it was Aizen who sent him to Soul Society. After the Bount attack on Seireitei Kariya manages to escape to another world, which accidentally)))) happens to be Lelouch's homeworld. Lelouch is ordered to go after him and kill him. He decides not catch the eye of acquaintances and calmly kill Kariya and return. After killing Kariya, he decides to visit С.С. and invite her to go with him, she will certainly agree and they become couple).
After defeating Aizen, Lelouch will often visit him in Muken to play chess and lead various philosophical discussions (how could it be without it))).
P.S. I really wish Unohana didn't die fighting Zaraki, as she's too interesting character for such a stupid death. Maybe even let her become Head Capitan after Yamamoto's death.
How will it go next... depends on author
Time in the home world of Lelouch and the Soul Society flows differently, very much))) At the moment when he is already 200 years old, only 5-7 years will pass in his world.
Pairing: Lelouch - C.C. of course))