I did put the Bleach tag on this, so I thought It'd be best to get this out there pretty quickly.
Have Isshin Kurosaki, Kisuke Urahara, Yoruichi Shihoin, Rukia Kukichi, Masaki Kurosaki and Kaien Shiba be reactors. Other than Kaien Shiba and the Espada, all of these reactors and the next ones I have about to mention should be experiencing this just before the events of Ichigo's birth. Kaien Shiba will be sent to the reaction theater just before his wife gets killed by a hollow. As for the other reactors, include all of the most notable Espada directly after they have sworn allegiance to Aizen, Yhwach and his Quincies, Aizen, any notable Shinigami captains and lieutenants, Yamamoto, and anyone else you want really. You can even include Zanpakuto spirits if you wish, such as Shirayuki or Muramasa. Perhaps even Kokuto. Regardless, I want the overseer of the reactors to be Hollow/Shiro Zangetsu and Tensa Zangetsu/younger Yhwach post TYBW arc. Please make sure to make the reactions realistic, varied, and true to the characters.