You are the earliest traitor of the Seireitei and the SECOND reason the Gotei 13 was made, a response to Yhwach and his army of Quincy, and you being the second reason.

After the second war and seeing how the old man Yamamoto bit the dust, you'd decide maybe it's time you should probably help since you'd be damned if you let Yhwach destroy what's been keeping threats from you so you can live however you want.

Of course due to this appearance of yours, only 3 people knew who you were, Shunsui Kyōraku and Jūshirō Ukitake who only knew you from what Yamamoto told them as he was their teacher and.. Retsu Unohana. A woman who you had a lot of history with as she fought you many, many times and hated you more and more for each time you spared her, she hated that she enjoyed fighting you more than even Zaraki when he was young and but a child.

After the war you would try to sneak away while everything was being repaired and rebuilt but as you were about to leave you saw Unohana standing there with her hands in the large sleeves of her robe and a cold look in her eyes.

"Why are you leaving so soon? You helped against Yhwach and Wandenreich afterall, by all means. Welcome back traitor." Unohana said in a neutral tone, clearly not being friendly but not outright bloodthirsty like you remember, you had noticed how she acted so kind and nice now after seeing her since about 1000ish years ago.

Though Unohana didn't know what to really do at that moment, she wanted to fight you like you both did much longer ago but she couldn't just kill baselessly anymore, this was a more peaceful era after all, no need for killers..

"Before you try to leave again, tell me one thing.. How did Yamamoto dying make you feel?" Unohana said in the same cold yet neutral tone, her hands not even reaching for her Zanpakutō, she wanted an answer that wasn't your usual one's, not one's full of arrogance from your immense strength.. Just you. The man before you became a traitor who she barely batted an eye at all those years ago.