Okay. I actually re-read everything. But I'm not sure I understand everything.
So this is basically my guess but I think what we saw in previous chapters was what people 'assumed' happen and we'll later get chapters that will show what actually happened. But again, that's just my guess.
So far I understand the guy being interviewed here is the same kid from the very first chapter. Chapter A. He mentioned in his narration how he grew up and noticed how nothing had happened to him ever since his friends disappeared.
So the significant people we know are:
1. First Guy, who's friends disappeared, who grew up without anything happen to him, who is contacted again by the reporter in the first chapter
2. The little girl who lived with 'God' who then possibly did the elementary school massacre, possibly the girl with the goldfish aquarium, might have mentioned something about wanting to remember
3. The fat NEET guy, who visited the shrine, who later is apparently killed/suicide
4. The Dream Guy, who dreamed about hanging up people, whose mother eventually got killed in a 'traffic accident', who turned off the bathwater
5. The Mom, a surviving parent of one of the massacre victims, who turned out to be abusive, who later killed Dream Guy's mom with her car
6. The mystery family in the Black Minivan, who appeared in the first chapter and possibly in the hospital one
7. The Teacher, whose wife is also a teacher, whose encounter in the hospital made his child named Makoto
8. The girls who went karaoke and found the old video by Takkun
9. The Ostracized Kid, who might have grew up to be Yuki Fukushima, the religious scholar, colleague to the writer/reporter, and also might be the founder of N that is being prisoned
10. The student girl who liked streams, who saw the college student closing the gap, possibly the one who liked to wave to the Factory Worker
11. The college student who streamed and then getting trolled by N about the gap
12. The Factory Worker who started waving at the student after buying bread and coffee at the convenience store
13. The guy who FaceTimed with the aquarium girl
Did I miss anyone?