"What was the accident?"
"After the experiment, we had no idea if it had been successful. Just as we were waiting for verification, the lab caught fire. Several of my colleagues were burned to death, including my sister and her husband. It happened on a day when I wasn't there. When I came back, Sisi told me the child had also died, and only Califa Arumi was rescued. After the children switched, they were always asleep. I didn't know whose child's soul I was holding in my arms, and I never got the chance to find out, because the child passed away from an illness that very night."
It all fit together now.
Mario Yuno remembered what Professor Liu Taylor had mentioned before, that Yuzo Joel clung to the dead child without letting go—that must have been the incident that occurred back then.
"Is Sisi Sonya Cornelle? My daughter-in-law is clearly alive. Why did she tell you she had been burned to death?"