[a] - Kumicho is a term that means 'Godfather', and those who hold its title serve as the head of the organization in the same way you might expect of a Mafia Godfather.
[b] - A Sakazuki ritual is a ceremony of exchanging sake cups in which one pledges loyalty to another and as a means of becoming family. There is a 5:5 pledge, in which the drinkers pledge loyalty to one another as equals and brothers, and a 7:3 pledge, in which drinkers pledge as Master and servant.
 - https://www.nippon.com/en/currents/d00205/yamaguchi-gumi-split-signals-changes-in-the-yakuza-world.html
 - https://www.britannica.com/biography/Taoka-Kazuo
 - https://asia.nikkei.com/Spotlight/My-Personal-History/Kenzo-Takada/Kenzo-Takada-3-From-aerial-attacks-to-rebuilding-among-burnt-out-ruins
 - https://en.wikipedia.org/wiki/Yama%E2%80%93Ichi_War
 - https://historica.fandom.com/wiki/Masahisa_Takenaka
 - https://www.tokyoreporter.com/crime/yakuza/japans-yakuza-groups-pay-tribute-to-yamaguchi-gumis-yoshinori-watanabe/
 - https://www.britannica.com/event/Kobe-earthquake-of-1995