Thread:HackerEX/@comment-43281069-20200106022111/@comment-43281069-20200111155623

Yep, it comes from "Battou", which means to draw one's sword and "Sai", which can also mean master or lord. It also doubles as a pun on "Batta", or grasshopper (which I just now changed it to after realizing I got the wrong insect for the joke I was trying to make).