User blog comment:Martialmaniac/Ten - Is it worth mentioning?/@comment-48285-20180417181148/@comment-5780397-20180418005853

The instructions are found inside the Southerpiece Auction catalog in chapter 85. Here we see Feitan enter through Ren (chap 123), and here Gon (chap 126). Also, here's Shalnark explining that Hatsu is the trigger (chap 134).