Are all the haibane suicides?
No. Reki is the only one who clearly killed herself in her former life. Although all the haibane names used in the show could be interpreted as some kind of suicide, there are far too many indications that this is not the case for me to agree with this theory. For starters, Reki is the only one born with black wings. She is set apart from the other haibane from the very first, and this continues throughout the show. She’s also the only one who displays any actual self-destructive behavior, her smoking. She also views the town very differently than the other haibane, who are rather happy there. Remember that in the Judeo-Christian tradition suicide is a major sin. This is why Reki was born with black wings. The other haibane were not. Rakka is kind of a special case, but I still don’t think she was a suicide, at least not in the same way Reki was. Reki threw herself in front of a train, but judging by Rakka’s reactions in the show, she more likely died from self-neglect. Whatever was tr