Ōetsu
Nimaiya

Ōetsu Nimaiya is the Third Officer of the Zero Division and the man who invented the Zanpakutō. Every Asauchi in Soul Society came out of his forge, which means every Shinigami who has ever drawn a sword is carrying his work, and the Gotei 13 exists in its current form because he made that possible.

He does not behave like it. Nimaiya arrives surrounded by an entourage, talks in slang, insists on elaborate formal greetings and then immediately undercuts them, and runs his domain as something closer to a nightclub than a workshop. When Ichigo Kurosaki and Renji Abarai turn up needing their broken swords remade, he throws Ichigo into a pit full of Asauchi and refuses to explain anything until Ichigo works it out himself.

The reveal in that pit reframes several hundred episodes. The Asauchi Ichigo bonds with takes the shape of his inner Hollow, because the Hollow was always the Shinigami half of him, and the old man in the coat was the Quincy half suppressing it. Nimaiya knew from the moment he saw the blade. His job is not to be kind about it, and the forge he lights afterwards produces the twin swords Ichigo carries for the rest of the war.