User blog comment:Kololz/Replace 'A' to 'Kou'?/@comment-115.66.40.193-20151001170414

Given that this wiki's pages are mainly written in English, Kou/Otsu/Hei won't make sense to people who don't know the romaji for  甲/乙/丙. Same reason why a significant number of people use Kai 2 instead of Kai Ni. "A" seems more convenient to type & easier to understand.