Hmm, I dunno. Kyouraku is much older than Byakuya and most definitely a senior to him as far as captaincy goes; he's also a noble, even if not a high noble like Byakuya. As for Zaraki, he's a monster of strength and power. So neither of them would work for this particular fic, because one of the very points I highlight is that Yumichika is lower than Byakuya on every level, and that this is an essential reason why Byakuya chose him as his master. I wrote him as needing someone who was not his superior in any way in real life, so really, it wouldn't work with Kyouraku or Zaraki.

Still, thank you very much for reading and commenting, and I'm glad you liked some of it anyway :)