"Among the disciples of the school of Nichi-ju, nobody should be chosen, directly or indirectly, as an heir disciple. However, anybody among the priests or the laymen of my congregation who spreads the teaching in Kyoto and who swears that other sects are the root of all evils and that only the Lotus Sutra leads to Buddhahood, only these people can be my disciples. And if candidates are equally gifted, they should propagate during the summer, practicing in turns. You should consider a person who spreads the teaching in this manner as the true disciple of Nichi-ju. So, in the days to come, this shall be my will."
The Third Year of Meitoku Mizunoe Saru January 29th  Seal of Nichi-ju
The Lotus Sutra itself chooses heir disciples, not the SGI, Kempon Hokke, nor Shamon Tsuchiya.