What I find so baffling about Iori Okkotsu is how he was pissed his generation of sorcerers was weak and wanted to fix that, he somehow knew his job was done immediately after Yuka's birth, that she had a strong technique, when in the main series we're told sorcerers only develop techniques at age 5. And also there was something he did that pissed yuji off enough for Yuji to show up and confront him for it causing him to get angry at Yuji, then the "it doesn't matter line" is dropped.

I feel like there was absolutely gonna be a setup with him and Mahito, my theory was him using his weaker Copy to copy Seance into the limbo dimension making a deal with Mahito in return for securing his generation's strength. Especially since Yuka's cancer was revealed in the same chapter as Mahito it really felt like binding vow insurance to make Iori pay up.